diff --git a/docs-developer/CHANGELOG-formats.md b/docs-developer/CHANGELOG-formats.md
index 6d1ed2b5c8..ecd794b08c 100644
--- a/docs-developer/CHANGELOG-formats.md
+++ b/docs-developer/CHANGELOG-formats.md
@@ -6,6 +6,14 @@ Note that this is not an exhaustive list. Processed profile format upgraders can
 
 ## Processed profile format
 
+### Version 70
+
+The `lib` column moved off the `resourceTable` and onto the `frameTable`. Previously a frame's library was reached indirectly, via `frame -> func -> resource -> lib`; now the frame points at its library directly, and `resourceTable` has no `lib` column at all. Frames with no library have their lib set to the `-1` sentinel.
+
+This decouples resources from libraries.
+
+The `lib` column can optionally be stored as an `Int32Array`, for profiles loaded from [JsonSlabs](https://github.com/mstange/json-slabs/) files (.jslb, .jslb.gz). Regular JS / JSON arrays are still accepted - but note that `-1` (not `null`) must be used regardless of format.
+
 ### Version 69
 
 A new marker schema display location, `timeline-network`, was added. A marker schema can list `timeline-network` in its `display` array to have markers of that type surfaced in the Network track.
diff --git a/profiler-cli/src/test/unit/call-tree-formatting.test.ts b/profiler-cli/src/test/unit/call-tree-formatting.test.ts
index db77920db4..28f0da1343 100644
--- a/profiler-cli/src/test/unit/call-tree-formatting.test.ts
+++ b/profiler-cli/src/test/unit/call-tree-formatting.test.ts
@@ -52,9 +52,8 @@ function buildTopDownResult(
   const state = store.getState();
   const threadSelectors = getThreadSelectors(0);
   const callTree = threadSelectors.getCallTree(state);
-  const libs = profile.libs;
 
-  const regularCallTree = collectCallTree(callTree, libs, options);
+  const regularCallTree = collectCallTree(callTree, options);
 
   return {
     type: 'thread-samples-top-down',
@@ -76,7 +75,6 @@ function buildBottomUpResult(
   const store = storeWithProfile(profile);
   const state = store.getState();
   const threadSelectors = getThreadSelectors(0);
-  const libs = profile.libs;
 
   // Build inverted call tree (bottom-up view)
   let collectedInvertedTree = null;
@@ -118,7 +116,7 @@ function buildBottomUpResult(
       weightType
     );
 
-    collectedInvertedTree = collectCallTree(invertedTree, libs, options);
+    collectedInvertedTree = collectCallTree(invertedTree, options);
   } catch (e) {
     // Failed to create inverted tree
     console.error('Failed to create inverted call tree:', e);
diff --git a/src/actions/profile-view.ts b/src/actions/profile-view.ts
index 80c350cfd9..6ef3391213 100644
--- a/src/actions/profile-view.ts
+++ b/src/actions/profile-view.ts
@@ -1949,7 +1949,6 @@ export function updateBottomBoxContentsAndMaybeOpen(
   bottomBoxInfo: BottomBoxInfo
 ): Action {
   const {
-    libIndex,
     sourceIndex,
     nativeSymbols,
     initialNativeSymbol,
@@ -1970,7 +1969,6 @@ export function updateBottomBoxContentsAndMaybeOpen(
 
   return {
     type: 'UPDATE_BOTTOM_BOX',
-    libIndex,
     sourceIndex,
     nativeSymbols,
     currentNativeSymbol: initialNativeSymbol,
diff --git a/src/app-logic/constants.ts b/src/app-logic/constants.ts
index 1f6b47f2d5..f8a4d98330 100644
--- a/src/app-logic/constants.ts
+++ b/src/app-logic/constants.ts
@@ -12,7 +12,7 @@ export const GECKO_PROFILE_VERSION = 36;
 // The current version of the "processed" profile format.
 // Please don't forget to update the processed profile format changelog in
 // `docs-developer/CHANGELOG-formats.md`.
-export const PROCESSED_PROFILE_VERSION = 69;
+export const PROCESSED_PROFILE_VERSION = 70;
 
 // The following are the margin sizes for the left and right of the timeline. Independent
 // components need to share these values.
diff --git a/src/app-logic/url-handling.ts b/src/app-logic/url-handling.ts
index 85a0b35e88..76475bf370 100644
--- a/src/app-logic/url-handling.ts
+++ b/src/app-logic/url-handling.ts
@@ -565,7 +565,6 @@ export function stateFromLocation(
     toValidTabSlug(pathParts[selectedTabPathPart]) || 'calltree';
   const sourceView: SourceViewState = {
     scrollGeneration: 0,
-    libIndex: null,
     sourceIndex: null,
     highlightedLine: null,
   };
diff --git a/src/profile-logic/bottom-box.ts b/src/profile-logic/bottom-box.ts
index cbd935ed8f..9ecc043399 100644
--- a/src/profile-logic/bottom-box.ts
+++ b/src/profile-logic/bottom-box.ts
@@ -2,8 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-import { ResourceType } from 'firefox-profiler/types';
-
 import type {
   Thread,
   IndexIntoStackTable,
@@ -37,14 +35,8 @@ export function getBottomBoxInfoForCallNode(
   thread: Thread,
   samples: SamplesLikeTable
 ): BottomBoxInfo {
-  const {
-    stackTable,
-    frameTable,
-    funcTable,
-    stringTable,
-    resourceTable,
-    nativeSymbols,
-  } = thread;
+  const { stackTable, frameTable, funcTable, stringTable, nativeSymbols } =
+    thread;
 
   const funcIndex = callNodeInfo.funcForNode(callNodeIndex);
   const { source: sourceIndex, line: funcLine } = getOriginalPositionForFrame(
@@ -54,11 +46,6 @@ export function getBottomBoxInfoForCallNode(
     funcTable,
     thread.sourceLocationTable
   );
-  const resource = funcTable.resource[funcIndex];
-  const libIndex =
-    resource !== -1 && resourceTable.type[resource] === ResourceType.Library
-      ? resourceTable.lib[resource]
-      : null;
   const callNodeFramePerStack = getCallNodeFramePerStack(
     callNodeIndex,
     callNodeInfo,
@@ -126,7 +113,6 @@ export function getBottomBoxInfoForCallNode(
   const hottestInstructionAddress = mapGetKeyWithMaxValue(addressTimings);
 
   return {
-    libIndex,
     sourceIndex,
     nativeSymbols: nativeSymbolInfosForCallNode,
     initialNativeSymbol:
@@ -148,14 +134,8 @@ export function getBottomBoxInfoForStackFrame(
   stackIndex: IndexIntoStackTable,
   thread: Thread
 ): BottomBoxInfo {
-  const {
-    stackTable,
-    frameTable,
-    funcTable,
-    resourceTable,
-    nativeSymbols,
-    stringTable,
-  } = thread;
+  const { stackTable, frameTable, funcTable, nativeSymbols, stringTable } =
+    thread;
 
   const frameIndex = stackTable.frame[stackIndex];
   const funcIndex = frameTable.func[frameIndex];
@@ -166,12 +146,6 @@ export function getBottomBoxInfoForStackFrame(
     funcTable,
     thread.sourceLocationTable
   );
-  const resource = funcTable.resource[funcIndex];
-  const libIndex =
-    resource !== -1 && resourceTable.type[resource] === ResourceType.Library
-      ? resourceTable.lib[resource]
-      : null;
-
   // Get native symbol for this frame
   const nativeSymbol = frameTable.nativeSymbol[frameIndex];
   const nativeSymbolInfos =
@@ -190,7 +164,6 @@ export function getBottomBoxInfoForStackFrame(
     nativeSymbol !== null ? frameTable.address[frameIndex] : -1;
 
   return {
-    libIndex,
     sourceIndex,
     nativeSymbols: nativeSymbolInfos,
     initialNativeSymbol: 0,
diff --git a/src/profile-logic/data-structures.ts b/src/profile-logic/data-structures.ts
index 1aa38d66fd..fa574aa539 100644
--- a/src/profile-logic/data-structures.ts
+++ b/src/profile-logic/data-structures.ts
@@ -35,6 +35,7 @@ import type {
   IndexIntoSubcategoryListForCategory,
   IndexIntoNativeSymbolTable,
   IndexIntoSourceLocationTable,
+  IndexIntoLibs,
   InnerWindowID,
   Address,
   Bytes,
@@ -117,6 +118,7 @@ export type RawFrameTableBuilder = {
   category: (IndexIntoCategoryList | null)[];
   subcategory: (IndexIntoSubcategoryListForCategory | null)[];
   func: IndexIntoFuncTable[];
+  lib: Array<IndexIntoLibs | -1>;
   nativeSymbol: (IndexIntoNativeSymbolTable | null)[];
   innerWindowID: (InnerWindowID | null)[];
   line: (number | null)[];
@@ -289,6 +291,7 @@ export function getRawFrameTableBuilder(): RawFrameTableBuilder {
     category: [],
     subcategory: [],
     func: [],
+    lib: [],
     nativeSymbol: [],
     innerWindowID: [],
     line: [],
@@ -311,6 +314,7 @@ export function getRawFrameTableBuilderWithExistingContents(
     category: frameTable.category.slice(),
     subcategory: frameTable.subcategory.slice(),
     func: Array.from(frameTable.func),
+    lib: Array.from(frameTable.lib),
     nativeSymbol: frameTable.nativeSymbol.slice(),
     innerWindowID: frameTable.innerWindowID.slice(),
     line: frameTable.line.slice(),
@@ -328,6 +332,7 @@ export function finishRawFrameTableBuilder(
     address: new Int32Array(builder.address),
     inlineDepth: new Uint8Array(builder.inlineDepth),
     func: new Int32Array(builder.func),
+    lib: new Int32Array(builder.lib),
   };
 }
 
@@ -409,7 +414,6 @@ export function getEmptyResourceTable(): ResourceTable {
     // If modifying this structure, please update all callers of this function to ensure
     // that they are pushing on correctly to the data structure. These pushes may not
     // be caught by the type system.
-    lib: [],
     name: [],
     host: [],
     type: [],
diff --git a/src/profile-logic/global-data-collector.ts b/src/profile-logic/global-data-collector.ts
index 03333b58c7..01ae67b233 100644
--- a/src/profile-logic/global-data-collector.ts
+++ b/src/profile-logic/global-data-collector.ts
@@ -61,8 +61,6 @@ export class GlobalDataCollector {
   _funcKeyToFuncIndex: Map<string, IndexIntoFuncTable> = new Map();
   _nativeSymbolKeyToNativeSymbolIndex: Map<string, IndexIntoNativeSymbolTable> =
     new Map();
-  _libIndexToResourceIndex: Map<IndexIntoLibs, IndexIntoResourceTable> =
-    new Map();
   _libNameToResourceIndex: Map<IndexIntoStringTable, IndexIntoResourceTable> =
     new Map();
   _originToResourceIndex: Map<string, IndexIntoResourceTable> = new Map();
@@ -179,7 +177,6 @@ export class GlobalDataCollector {
 
         const idIndex = this._stringTable.indexForString(extensions.id[i]);
 
-        resourceTable.lib[resourceIndex] = null;
         resourceTable.name[resourceIndex] =
           this._stringTable.indexForString(name);
         resourceTable.host[resourceIndex] = idIndex;
@@ -223,7 +220,6 @@ export class GlobalDataCollector {
     this._originToResourceIndex.set(origin, resourceIndex);
     if (host) {
       // This is a webhost URL.
-      resourceTable.lib[resourceIndex] = null;
       resourceTable.name[resourceIndex] =
         this._stringTable.indexForString(origin);
       resourceTable.host[resourceIndex] =
@@ -232,7 +228,6 @@ export class GlobalDataCollector {
     } else {
       // This is a URL, but it doesn't point to something on the web, e.g. a
       // chrome url.
-      resourceTable.lib[resourceIndex] = null;
       resourceTable.name[resourceIndex] =
         this._stringTable.indexForString(scriptURI);
       resourceTable.host[resourceIndex] = null;
@@ -241,26 +236,7 @@ export class GlobalDataCollector {
     return resourceIndex;
   }
 
-  indexForLibResource(libIndex: IndexIntoLibs): IndexIntoResourceTable {
-    let resourceIndex = this._libIndexToResourceIndex.get(libIndex);
-    if (resourceIndex !== undefined) {
-      return resourceIndex;
-    }
-
-    const resourceTable = this._resourceTable;
-
-    resourceIndex = this._resourceTable.length++;
-    this._libIndexToResourceIndex.set(libIndex, resourceIndex);
-    resourceTable.lib[resourceIndex] = libIndex;
-    resourceTable.name[resourceIndex] = this._stringTable.indexForString(
-      this._libs[libIndex].name
-    );
-    resourceTable.host[resourceIndex] = null;
-    resourceTable.type[resourceIndex] = ResourceType.Library;
-    return resourceIndex;
-  }
-
-  indexForNameOnlyLibResource(
+  indexForLibResourceByName(
     libNameStringIndex: IndexIntoStringTable
   ): IndexIntoResourceTable {
     let resourceIndex = this._libNameToResourceIndex.get(libNameStringIndex);
@@ -272,13 +248,18 @@ export class GlobalDataCollector {
 
     resourceIndex = this._resourceTable.length++;
     this._libNameToResourceIndex.set(libNameStringIndex, resourceIndex);
-    resourceTable.lib[resourceIndex] = null;
     resourceTable.name[resourceIndex] = libNameStringIndex;
     resourceTable.host[resourceIndex] = null;
     resourceTable.type[resourceIndex] = ResourceType.Library;
     return resourceIndex;
   }
 
+  indexForLibResourceByLib(libIndex: IndexIntoLibs): IndexIntoResourceTable {
+    return this.indexForLibResourceByName(
+      this._stringTable.indexForString(this._libs[libIndex].name)
+    );
+  }
+
   indexForNativeSymbol(
     libIndex: IndexIntoLibs,
     address: Address,
diff --git a/src/profile-logic/import/chrome.ts b/src/profile-logic/import/chrome.ts
index 0a448666e0..eba5e6879c 100644
--- a/src/profile-logic/import/chrome.ts
+++ b/src/profile-logic/import/chrome.ts
@@ -699,6 +699,7 @@ async function processTracingEvents(
           frameTable.category[frameIndex] = category;
           frameTable.subcategory[frameIndex] = 0;
           frameTable.func[frameIndex] = funcId;
+          frameTable.lib[frameIndex] = -1;
           frameTable.nativeSymbol[frameIndex] = null;
           frameTable.innerWindowID[frameIndex] = 0;
           frameTable.line[frameIndex] =
diff --git a/src/profile-logic/import/dhat.ts b/src/profile-logic/import/dhat.ts
index e0dd3f240c..94c9cc859e 100644
--- a/src/profile-logic/import/dhat.ts
+++ b/src/profile-logic/import/dhat.ts
@@ -212,6 +212,7 @@ export function attemptToConvertDhat(json: unknown): Profile | null {
   frameTable.category.push(otherCategory);
   frameTable.subcategory.push(otherSubCategory);
   frameTable.innerWindowID.push(null);
+  frameTable.lib.push(-1);
   frameTable.nativeSymbol.push(null);
   frameTable.inlineDepth.push(0);
   frameTable.func.push(rootFuncIndex);
@@ -279,6 +280,7 @@ export function attemptToConvertDhat(json: unknown): Profile | null {
     frameTable.category.push(otherCategory);
     frameTable.subcategory.push(otherSubCategory);
     frameTable.innerWindowID.push(null);
+    frameTable.lib.push(-1);
     frameTable.nativeSymbol.push(null);
     frameTable.inlineDepth.push(0);
     frameTable.func.push(funcIndex);
diff --git a/src/profile-logic/import/flame-graph.ts b/src/profile-logic/import/flame-graph.ts
index 6a7e4a1fff..71504573b1 100644
--- a/src/profile-logic/import/flame-graph.ts
+++ b/src/profile-logic/import/flame-graph.ts
@@ -120,6 +120,7 @@ export function convertFlameGraphProfile(profileText: string): Profile {
     frameTable.category.push(category);
     frameTable.subcategory.push(0);
     frameTable.func.push(funcIndex);
+    frameTable.lib.push(-1);
     frameTable.nativeSymbol.push(null);
     frameTable.innerWindowID.push(null);
     frameTable.line.push(null);
diff --git a/src/profile-logic/import/simpleperf.ts b/src/profile-logic/import/simpleperf.ts
index 75fce1f0d9..39be0d9fb2 100644
--- a/src/profile-logic/import/simpleperf.ts
+++ b/src/profile-logic/import/simpleperf.ts
@@ -99,7 +99,6 @@ class FirefoxResourceTable {
   findOrAddResource(file: report.IFile): IndexIntoResourceTable {
     let resourceIndex = this.resourcesMap.get(file.id!);
     if (!resourceIndex) {
-      this.resourceTable.lib.push(null);
       this.resourceTable.name.push(this.strings.indexForString(file.path!));
       this.resourceTable.host.push(null);
       this.resourceTable.type.push(1); // Library
@@ -177,6 +176,7 @@ class FirefoxFrameTable {
       this.frameTable.category.push(category);
       this.frameTable.subcategory.push(0);
       this.frameTable.func.push(funcIndex);
+      this.frameTable.lib.push(-1);
       this.frameTable.nativeSymbol.push(null);
       this.frameTable.innerWindowID.push(null);
       this.frameTable.line.push(null);
diff --git a/src/profile-logic/insert-stack-labels.ts b/src/profile-logic/insert-stack-labels.ts
index e614569e82..988a30cb23 100644
--- a/src/profile-logic/insert-stack-labels.ts
+++ b/src/profile-logic/insert-stack-labels.ts
@@ -136,6 +136,7 @@ export function insertStackLabels(
     frameTable.func[frameIndex] = funcIndex;
     frameTable.category[frameIndex] = labelCategoryIndex;
     frameTable.subcategory[frameIndex] = 0;
+    frameTable.lib[frameIndex] = -1;
     frameTable.nativeSymbol[frameIndex] = null;
     frameTable.address[frameIndex] = 0;
     frameTable.inlineDepth[frameIndex] = 0;
diff --git a/src/profile-logic/js-tracer.ts b/src/profile-logic/js-tracer.ts
index 92ef451f82..2ad48571c2 100644
--- a/src/profile-logic/js-tracer.ts
+++ b/src/profile-logic/js-tracer.ts
@@ -610,6 +610,7 @@ export function convertJsTracerToThreadWithoutSamples(
     frameTable.inlineDepth.push(0);
     frameTable.category.push(otherCategory);
     frameTable.func.push(funcIndex);
+    frameTable.lib.push(-1);
     frameTable.nativeSymbol.push(null);
     frameTable.innerWindowID.push(0);
     frameTable.line.push(line);
diff --git a/src/profile-logic/merge-compare.ts b/src/profile-logic/merge-compare.ts
index 10e6a3fd14..18e8e7518a 100644
--- a/src/profile-logic/merge-compare.ts
+++ b/src/profile-logic/merge-compare.ts
@@ -461,11 +461,7 @@ export function mergeSharedData(profiles: Profile[]): {
   const {
     resourceTable: newResourceTable,
     translationMaps: translationMapsForResources,
-  } = mergeResourceTables(
-    profiles,
-    translationMapsForStrings,
-    translationMapsForLibs
-  );
+  } = mergeResourceTables(profiles, translationMapsForStrings);
   const {
     nativeSymbols: newNativeSymbols,
     translationMaps: translationMapsForNativeSymbols,
@@ -490,7 +486,8 @@ export function mergeSharedData(profiles: Profile[]): {
     translationMapsForFuncs,
     translationMapsForNativeSymbols,
     translationMapsForOriginalLocation,
-    translationMapsForCategories
+    translationMapsForCategories,
+    translationMapsForLibs
   );
   const {
     stackTable: newStackTable,
@@ -721,7 +718,7 @@ function mergeLibs(libsPerProfile: Lib[][]): {
     const oldLibToNewLibPlusOne = new Int32Array(libs.length);
 
     libs.forEach((lib, i) => {
-      const insertedLibKey = [lib.name, lib.debugName].join('#');
+      const insertedLibKey = [lib.debugName, lib.breakpadId].join('#');
       const insertedLibIndex = mapOfInsertedLibs.get(insertedLibKey);
       if (insertedLibIndex !== undefined) {
         oldLibToNewLibPlusOne[i] = insertedLibIndex + 1;
@@ -747,11 +744,14 @@ function _mapLib(
   return oldLibToNewLibPlusOne[libIndex] - 1;
 }
 
-function _mapNullableLib(
-  libIndex: IndexIntoLibs | null,
+function _mapFrameLib(
+  libIndex: IndexIntoLibs | -1,
   oldLibToNewLibPlusOne: TranslationMapForLibs
-): IndexIntoLibs | null {
-  return libIndex !== null ? oldLibToNewLibPlusOne[libIndex] - 1 : null;
+): IndexIntoLibs | -1 {
+  if (libIndex === -1) {
+    return -1;
+  }
+  return oldLibToNewLibPlusOne[libIndex] - 1;
 }
 
 function _mapString(
@@ -846,8 +846,7 @@ function _mapNullableStack(
  */
 function mergeResourceTables(
   profiles: ReadonlyArray<Profile>,
-  translationMapsForStrings: TranslationMapForStrings[],
-  translationMapsForLibs: TranslationMapForLibs[]
+  translationMapsForStrings: TranslationMapForStrings[]
 ): {
   resourceTable: ResourceTable;
   translationMaps: TranslationMapForResources[];
@@ -857,7 +856,6 @@ function mergeResourceTables(
   const newResourceTable = getEmptyResourceTable();
 
   profiles.forEach((profile, profileIndex) => {
-    const oldLibToNewLibPlusOne = translationMapsForLibs[profileIndex];
     const oldStringToNewStringPlusOne = translationMapsForStrings[profileIndex];
     const { resourceTable } = profile.shared;
     const oldResourceToNewResourcePlusOne = new Int32Array(
@@ -865,10 +863,6 @@ function mergeResourceTables(
     );
 
     for (let i = 0; i < resourceTable.length; i++) {
-      const libIndex = _mapNullableLib(
-        resourceTable.lib[i],
-        oldLibToNewLibPlusOne
-      );
       const nameIndex = _mapString(
         resourceTable.name[i],
         oldStringToNewStringPlusOne
@@ -890,7 +884,6 @@ function mergeResourceTables(
       oldResourceToNewResourcePlusOne[i] = newResourceTable.length + 1;
       mapOfInsertedResources.set(resourceKey, newResourceTable.length);
 
-      newResourceTable.lib.push(libIndex);
       newResourceTable.name.push(nameIndex);
       newResourceTable.host.push(hostIndex);
       newResourceTable.type.push(type);
@@ -1059,7 +1052,8 @@ function mergeFrameTables(
   translationMapsForFuncs: TranslationMapForFuncs[],
   translationMapsForNativeSymbols: TranslationMapForNativeSymbols[],
   translationMapsForOriginalLocation: TranslationMapForOriginalLocation[],
-  translationMapsForCategories: TranslationMapForCategories[]
+  translationMapsForCategories: TranslationMapForCategories[],
+  translationMapsForLibs: TranslationMapForLibs[]
 ): { frameTable: RawFrameTable; translationMaps: TranslationMapForFrames[] } {
   const translationMaps: TranslationMapForFrames[] = [];
   const newFrameTable = getRawFrameTableBuilder();
@@ -1073,6 +1067,7 @@ function mergeFrameTables(
       translationMapsForOriginalLocation[profileIndex];
     const oldCategoryToNewCategoryPlusOne =
       translationMapsForCategories[profileIndex];
+    const oldLibToNewLibPlusOne = translationMapsForLibs[profileIndex];
     const oldFrameToNewFramePlusOne = new Int32Array(frameTable.length);
 
     for (let i = 0; i < frameTable.length; i++) {
@@ -1094,6 +1089,9 @@ function mergeFrameTables(
       newFrameTable.subcategory.push(subcategory);
       newFrameTable.nativeSymbol.push(nativeSymbol);
       newFrameTable.func.push(func);
+      newFrameTable.lib.push(
+        _mapFrameLib(frameTable.lib[i], oldLibToNewLibPlusOne)
+      );
       newFrameTable.innerWindowID.push(frameTable.innerWindowID[i]);
       newFrameTable.line.push(frameTable.line[i]);
       newFrameTable.column.push(frameTable.column[i]);
diff --git a/src/profile-logic/process-profile.ts b/src/profile-logic/process-profile.ts
index 69c4712e7a..a5ad586acb 100644
--- a/src/profile-logic/process-profile.ts
+++ b/src/profile-logic/process-profile.ts
@@ -116,6 +116,7 @@ import type {
   GeckoSourceTable,
   IndexIntoCategoryList,
   IndexIntoFrameTable,
+  IndexIntoLibs,
   CounterDisplayConfig,
   RawProfileSharedData,
 } from 'firefox-profiler/types';
@@ -202,7 +203,11 @@ type ExtractionInfo = {
   addressLocator: AddressLocator;
   stringToNewFuncIndexAndFrameAddress: Map<
     string,
-    { funcIndex: IndexIntoFuncTable; frameAddress: Address | null }
+    {
+      funcIndex: IndexIntoFuncTable;
+      frameAddress: Address | null;
+      libIndex: IndexIntoLibs | null;
+    }
   >;
   globalDataCollector: GlobalDataCollector;
   geckoSourceTable: GeckoSourceTable;
@@ -226,6 +231,7 @@ export function extractFuncsAndResourcesFromFrameLocations(
 ): {
   frameFuncs: IndexIntoFuncTable[];
   frameAddresses: (Address | null)[];
+  frameLibs: (IndexIntoLibs | null)[];
 } {
   const stringTable = globalDataCollector.getStringTable();
 
@@ -242,6 +248,7 @@ export function extractFuncsAndResourcesFromFrameLocations(
   // information by applying various string matching heuristics.
   const frameFuncs = [];
   const frameAddresses = [];
+  const frameLibs: (IndexIntoLibs | null)[] = [];
   for (let frameIndex = 0; frameIndex < frameLocations.length; frameIndex++) {
     const originalLocationIndex = frameLocations[frameIndex];
     const locationString = ensureExists(
@@ -253,9 +260,10 @@ export function extractFuncsAndResourcesFromFrameLocations(
       extractionInfo.stringToNewFuncIndexAndFrameAddress.get(locationString);
     if (info !== undefined) {
       // The location string was already processed.
-      const { funcIndex, frameAddress } = info;
+      const { funcIndex, frameAddress, libIndex } = info;
       frameFuncs.push(funcIndex);
       frameAddresses.push(frameAddress);
+      frameLibs.push(libIndex);
       continue;
     }
 
@@ -263,6 +271,7 @@ export function extractFuncsAndResourcesFromFrameLocations(
     // resource information.
     let funcIndex = null;
     let frameAddress = null;
+    let libIndex: IndexIntoLibs | null = null;
     const unsymbolicatedInfo = _extractUnsymbolicatedFunction(
       extractionInfo,
       locationString,
@@ -271,6 +280,7 @@ export function extractFuncsAndResourcesFromFrameLocations(
     if (unsymbolicatedInfo !== null) {
       funcIndex = unsymbolicatedInfo.funcIndex;
       frameAddress = unsymbolicatedInfo.frameAddress;
+      libIndex = unsymbolicatedInfo.libIndex;
     } else {
       funcIndex = _extractCppFunction(extractionInfo, locationString);
       if (funcIndex === null) {
@@ -289,15 +299,18 @@ export function extractFuncsAndResourcesFromFrameLocations(
     extractionInfo.stringToNewFuncIndexAndFrameAddress.set(locationString, {
       funcIndex,
       frameAddress,
+      libIndex,
     });
 
     frameFuncs.push(funcIndex);
     frameAddresses.push(frameAddress);
+    frameLibs.push(libIndex);
   }
 
   return {
     frameFuncs,
     frameAddresses,
+    frameLibs,
   };
 }
 
@@ -308,23 +321,25 @@ export function extractFuncsAndResourcesFromFrameLocations(
  * into the same function, so cannot do any function grouping. So we get one "function" per
  * address.
  * We also associate the address with the library that contains it, and convert the address
- * into a library-relative offset. This association is established via the function's
- * "resource": The function points to the resource (of type ResourceType.Library), and the
- * resource has the index to the library in thread.libs.
- * We return the index of the newly-added function, and the address as a library-relative
- * offset.
+ * into a library-relative offset. The library index goes onto the frame (frameTable.lib);
+ * and the function additionally gets a "resource" of type ResourceType.Library.
  */
 function _extractUnsymbolicatedFunction(
   extractionInfo: ExtractionInfo,
   locationString: string,
   locationIndex: IndexIntoStringTable
-): { funcIndex: IndexIntoFuncTable; frameAddress: Address } | null {
+): {
+  funcIndex: IndexIntoFuncTable;
+  frameAddress: Address;
+  libIndex: IndexIntoLibs | null;
+} | null {
   if (!locationString.startsWith('0x')) {
     return null;
   }
   const { addressLocator, globalDataCollector } = extractionInfo;
 
   let resourceIndex = -1;
+  let libIndex: IndexIntoLibs | null = null;
   let addressRelativeToLib: Address = -1;
 
   try {
@@ -343,8 +358,8 @@ function _extractUnsymbolicatedFunction(
       // Yes, we found the library whose mapping covers this address!
       addressRelativeToLib = relativeAddress;
 
-      const libIndex = globalDataCollector.indexForLib(lib);
-      resourceIndex = globalDataCollector.indexForLibResource(libIndex);
+      libIndex = globalDataCollector.indexForLib(lib);
+      resourceIndex = globalDataCollector.indexForLibResourceByLib(libIndex);
     }
   } catch (_e) {
     // Probably a hex parse error. Ignore.
@@ -359,7 +374,7 @@ function _extractUnsymbolicatedFunction(
     null,
     null
   );
-  return { funcIndex, frameAddress: addressRelativeToLib };
+  return { funcIndex, frameAddress: addressRelativeToLib, libIndex };
 }
 
 /**
@@ -401,7 +416,7 @@ function _extractCppFunction(
     return frameInfo.funcIndex;
   }
 
-  const resourceIndex = globalDataCollector.indexForNameOnlyLibResource(
+  const resourceIndex = globalDataCollector.indexForLibResourceByName(
     libraryNameStringIndex
   );
   return globalDataCollector.indexForFunc(
@@ -535,7 +550,8 @@ function _processFrameTable(
   geckoFrameStruct: GeckoFrameStruct,
   sharedFrameTable: RawFrameTableBuilder,
   frameFuncs: IndexIntoFuncTable[],
-  frameAddresses: (Address | null)[]
+  frameAddresses: (Address | null)[],
+  frameLibs: (IndexIntoLibs | null)[]
 ): IndexIntoFrameTable {
   const frameIndexOffset = sharedFrameTable.length;
   for (let i = 0; i < geckoFrameStruct.length; i++) {
@@ -545,6 +561,7 @@ function _processFrameTable(
     sharedFrameTable.category[newIndex] = geckoFrameStruct.category[i];
     sharedFrameTable.subcategory[newIndex] = geckoFrameStruct.subcategory[i];
     sharedFrameTable.func[newIndex] = frameFuncs[i];
+    sharedFrameTable.lib[newIndex] = frameLibs[i] ?? -1;
     sharedFrameTable.nativeSymbol[newIndex] = null;
     sharedFrameTable.innerWindowID[newIndex] =
       geckoFrameStruct.innerWindowID[i];
@@ -1327,7 +1344,7 @@ function _processThread(
   const { libs, pausedRanges, meta, sources } = processProfile;
   const { shutdownTime } = meta;
 
-  const { frameFuncs, frameAddresses } =
+  const { frameFuncs, frameAddresses, frameLibs } =
     extractFuncsAndResourcesFromFrameLocations(
       geckoFrameStruct.location,
       geckoFrameStruct.relevantForJS,
@@ -1341,7 +1358,8 @@ function _processThread(
     geckoFrameStruct,
     globalDataCollector.getFrameTable(),
     frameFuncs,
-    frameAddresses
+    frameAddresses,
+    frameLibs
   );
   const stackIndexOffset = _processStackTable(
     geckoStackTable,
@@ -2113,6 +2131,7 @@ function convertSharedTablesEligibleColumns(
       address: toInt32Array(frameTable.address),
       inlineDepth: toUint8Array(frameTable.inlineDepth),
       func: toInt32Array(frameTable.func),
+      lib: toInt32Array(frameTable.lib),
     },
   };
 }
diff --git a/src/profile-logic/processed-profile-versioning.ts b/src/profile-logic/processed-profile-versioning.ts
index 0999f5c078..89d5e4e2f9 100644
--- a/src/profile-logic/processed-profile-versioning.ts
+++ b/src/profile-logic/processed-profile-versioning.ts
@@ -3310,6 +3310,29 @@ const _upgraders: {
       }
     }
   },
+  [70]: (profile: any) => {
+    // The `lib` column moved off the resourceTable and onto the frameTable, so
+    // that resources and libraries can vary independently: multiple libs can
+    // now share one resource.
+    //
+    // Before: frame -> func -> resource -> lib
+    // After:  frame -> lib
+    // Frames with no library use the sentinel value -1.
+    const { frameTable, funcTable, resourceTable } = profile.shared;
+    const libForFunc = new Int32Array(funcTable.length).fill(-1);
+    for (let funcIndex = 0; funcIndex < funcTable.length; funcIndex++) {
+      const resourceIndex = funcTable.resource[funcIndex];
+      if (resourceIndex !== -1) {
+        libForFunc[funcIndex] = resourceTable.lib[resourceIndex] ?? -1;
+      }
+    }
+    const lib = new Array(frameTable.length).fill(-1);
+    for (let frameIndex = 0; frameIndex < frameTable.length; frameIndex++) {
+      lib[frameIndex] = libForFunc[frameTable.func[frameIndex]];
+    }
+    frameTable.lib = lib;
+    delete resourceTable.lib;
+  },
   // If you add a new upgrader here, please document the change in
   // `docs-developer/CHANGELOG-formats.md`.
 };
diff --git a/src/profile-logic/profile-compacting.ts b/src/profile-logic/profile-compacting.ts
index c7c59ce82b..90eb76dfc7 100644
--- a/src/profile-logic/profile-compacting.ts
+++ b/src/profile-logic/profile-compacting.ts
@@ -50,6 +50,10 @@ type ColumnDescription<TCol> = null extends (
   : Int32Array<ArrayBuffer> extends TCol
     ?
         | { type: 'INDEX_REF_INT32'; referencedTable: TableCompactionState }
+        | {
+            type: 'INDEX_REF_OR_NEG_ONE_INT32';
+            referencedTable: TableCompactionState;
+          }
         | { type: 'SELF_RELATIVE_PARENT' }
         | { type: 'NO_REF' }
     :
@@ -88,6 +92,10 @@ const ColDesc = {
     type: 'INDEX_REF_OR_NEG_ONE' as const,
     referencedTable,
   }),
+  indexRefOrNegOneInt32: (referencedTable: TableCompactionState) => ({
+    type: 'INDEX_REF_OR_NEG_ONE_INT32' as const,
+    referencedTable,
+  }),
   selfPrefixOffset: () => ({ type: 'SELF_RELATIVE_PARENT' as const }),
   noRef: () => ({ type: 'NO_REF' as const }),
 };
@@ -170,6 +178,7 @@ export function computeCompactedProfile(
     category: ColDesc.noRef(),
     subcategory: ColDesc.noRef(),
     func: ColDesc.indexRefInt32(tcs.funcTable),
+    lib: ColDesc.indexRefOrNegOneInt32(tcs.libs),
     nativeSymbol: ColDesc.indexRefOrNull(tcs.nativeSymbols),
     innerWindowID: ColDesc.noRef(),
     line: ColDesc.noRef(),
@@ -194,7 +203,6 @@ export function computeCompactedProfile(
   const resourceTableDesc: TableDescription<ResourceTable> = {
     name: ColDesc.indexRef(tcs.stringArray),
     host: ColDesc.indexRefOrNull(tcs.stringArray),
-    lib: ColDesc.indexRefOrNull(tcs.libs),
     type: ColDesc.noRef(),
   };
   const nativeSymbolsDesc: TableDescription<NativeSymbolTable> = {
@@ -355,6 +363,7 @@ function _markTableAndComputeTranslation<T>(
       case 'SELF_RELATIVE_PARENT':
         break; // already handled in the first pass
       case 'INDEX_REF_OR_NEG_ONE':
+      case 'INDEX_REF_OR_NEG_ONE_INT32':
         markColumnWithNegOneableFields(
           col,
           markBuffer,
@@ -419,10 +428,12 @@ function markSelfColumnPrefixOffset(
 }
 
 function markColumnWithNegOneableFields(
-  col: Array<number | -1>,
+  col: Array<number | -1> | Int32Array<ArrayBuffer>,
   shouldMark: BitSet,
   markBuf: BitSet
 ) {
+  // Polymorphic: indexing works the same on Int32Array as on number[], so the
+  // INDEX_REF_OR_NEG_ONE and INDEX_REF_OR_NEG_ONE_INT32 cases share this function.
   for (let i = 0; i < col.length; i++) {
     if (checkBit(shouldMark, i)) {
       const val = col[i];
@@ -554,6 +565,14 @@ function _compactTable<T extends { length: number }>(
           newLength
         );
         break;
+      case 'INDEX_REF_OR_NEG_ONE_INT32':
+        result[key] = _compactColIndexOrNegOneInt32(
+          oldCol,
+          markBuffer,
+          desc.referencedTable.oldIndexToNewIndexPlusOne,
+          newLength
+        );
+        break;
       case 'NO_REF':
         result[key] = _compactColCopy(oldCol, markBuffer, newLength);
         break;
@@ -646,6 +665,23 @@ function _compactColIndexOrNegOne(
   return newCol;
 }
 
+function _compactColIndexOrNegOneInt32(
+  oldCol: Array<number | -1> | Int32Array<ArrayBuffer>,
+  markBuffer: BitSet,
+  oldIndexToNewIndexPlusOne: Int32Array,
+  newLength: number
+): Int32Array<ArrayBuffer> {
+  const newCol = new Int32Array(newLength);
+  let newIndex = 0;
+  for (let i = 0; i < oldCol.length; i++) {
+    if (checkBit(markBuffer, i)) {
+      const val = oldCol[i];
+      newCol[newIndex++] = val !== -1 ? oldIndexToNewIndexPlusOne[val] - 1 : -1;
+    }
+  }
+  return newCol;
+}
+
 function _compactColSelfPrefixOffset(
   oldCol: Int32Array<ArrayBuffer>,
   markBuffer: BitSet,
diff --git a/src/profile-logic/profile-data.ts b/src/profile-logic/profile-data.ts
index be33781b78..bfc600d87f 100644
--- a/src/profile-logic/profile-data.ts
+++ b/src/profile-logic/profile-data.ts
@@ -4358,6 +4358,7 @@ export function nudgeReturnAddresses(profile: Profile): Profile {
       newFrameTable.category.push(frameTable.category[frame]);
       newFrameTable.subcategory.push(frameTable.subcategory[frame]);
       newFrameTable.func.push(frameTable.func[frame]);
+      newFrameTable.lib.push(frameTable.lib[frame]);
       newFrameTable.nativeSymbol.push(frameTable.nativeSymbol[frame]);
       newFrameTable.innerWindowID.push(frameTable.innerWindowID[frame]);
       newFrameTable.line.push(frameTable.line[frame]);
@@ -4453,7 +4454,7 @@ export function findAddressProofForFile(
   sourceIndex: IndexIntoSourceTable
 ): AddressProof | null {
   const { libs } = profile;
-  const { frameTable, funcTable, resourceTable } = profile.shared;
+  const { frameTable, funcTable } = profile.shared;
   const func = funcTable.source.indexOf(sourceIndex);
   if (func === -1) {
     return null;
@@ -4463,15 +4464,11 @@ export function findAddressProofForFile(
     return null;
   }
   const address = frameTable.address[frame];
-  if (address === null) {
+  if (address === -1) {
     return null;
   }
-  const resource = funcTable.resource[func];
-  if (resourceTable.type[resource] !== ResourceType.Library) {
-    return null;
-  }
-  const libIndex = resourceTable.lib[resource];
-  if (libIndex === null) {
+  const libIndex = frameTable.lib[frame];
+  if (libIndex === -1) {
     return null;
   }
   const lib = libs[libIndex];
@@ -4768,6 +4765,7 @@ export function computeFrameTableFromRawFrameTable(
     category: rawFrameTable.category,
     subcategory: rawFrameTable.subcategory,
     func,
+    lib: toInt32Array(rawFrameTable.lib),
     nativeSymbol: rawFrameTable.nativeSymbol,
     innerWindowID: rawFrameTable.innerWindowID,
     line: rawFrameTable.line,
diff --git a/src/profile-logic/sanitize.ts b/src/profile-logic/sanitize.ts
index 9bba0aedc4..81a78c1032 100644
--- a/src/profile-logic/sanitize.ts
+++ b/src/profile-logic/sanitize.ts
@@ -257,7 +257,6 @@ export function sanitizePII(
       if (resourcesToBeSanitized.size) {
         const newResourceTable = (newShared.resourceTable = {
           ...resourceTable,
-          lib: resourceTable.lib.slice(),
           name: resourceTable.name.slice(),
           host: resourceTable.host.slice(),
         });
@@ -272,7 +271,6 @@ export function sanitizePII(
               `<Resource #${resourceIndex}>`
             );
             newResourceTable.name[resourceIndex] = name;
-            newResourceTable.lib[resourceIndex] = null;
             newResourceTable.host[resourceIndex] = null;
           }
         }
diff --git a/src/profile-logic/symbolication.ts b/src/profile-logic/symbolication.ts
index b0c8d1d7e6..5ba00ad5e0 100644
--- a/src/profile-logic/symbolication.ts
+++ b/src/profile-logic/symbolication.ts
@@ -31,7 +31,6 @@ import type {
   CallNodePath,
   Lib,
 } from 'firefox-profiler/types';
-import { ResourceType } from 'firefox-profiler/types';
 import type {
   AbstractSymbolStore,
   AddressResult,
@@ -119,9 +118,13 @@ import { updateRawThreadStacks } from './profile-data';
  *    It also creates a nativeSymbols table but leaves it completely empty.
  *  - The frame and its func both get their address field set to the
  *    library-relative offset.
- *  - The func's resource field is set to a resource of type "library" that
- *    points to the lib object in the thread's "libs" list that contained this
- *    address. The frame's and func's address fields are relative to that lib.
+ *  - The frame's lib field is set to the index of the containing library in
+ *    profile.libs. The frame's address field is relative to that lib.
+ *    Symbolication groups frames by this field.
+ *  - The func's resource field is set to a resource of type "library" with the
+ *    name of the library. Multiple libraries with the same name can exist and
+ *    they will share the same resource, for example in a merged profile from
+ *    two different builds of the same library.
  *  - All frames start out with their nativeSymbol field set to null.
  *  - All return addresses are adjusted by subtracting one byte, to point into
  *    the call instruction. See nudgeReturnAddresses for details.
@@ -208,8 +211,9 @@ export type SymbolicationStepCallback = (
 ) => void;
 
 type ProfileLibSymbolicationInfo = {
-  // The resourceIndex for this lib in this thread.
-  resourceIndex: IndexIntoResourceTable;
+  // The resource to give to funcs which are newly created for this lib, or -1
+  // if this lib's frames have no resource. Multiple libs can share a resource.
+  resourceIndex: IndexIntoResourceTable | -1;
   // The libIndex for this lib in this thread.
   libIndex: IndexIntoLibs;
   // The set of funcs for this lib in this thread.
@@ -283,78 +287,107 @@ function makeConsensusMap<K, V>(
 /**
  * Gather the symbols needed in this thread, and some auxiliary information that
  * allows the symbol substitation step at the end to work efficiently.
- * Returns a map with one entry for each library resource.
+ * Returns a map with one entry for each library that has frames in the profile.
  */
 function getSymbolicationInfo(
   shared: RawProfileSharedData,
   libs: Lib[]
 ): ProfileSymbolicationInfo {
-  const { frameTable, funcTable, nativeSymbols, resourceTable } = shared;
+  const { frameTable, funcTable, nativeSymbols } = shared;
 
-  const map = new Map<string, ProfileLibSymbolicationInfo>();
-  for (
-    let resourceIndex = 0;
-    resourceIndex < resourceTable.length;
-    resourceIndex++
-  ) {
-    const resourceType = resourceTable.type[resourceIndex];
-    if (resourceType !== ResourceType.Library) {
+  // Pass 1 over the frames: group frames (and their addresses) by library, and
+  // work out which library each func belongs to.
+  //
+  // A func can be referenced by frames from more than one library, for example
+  // when two builds of the same library share a resource and symbolication has
+  // resolved frames from both builds to the same name. Such a func must not be
+  // recycled by either library, so we mark it with FUNC_LIB_SHARED.
+  const FUNC_LIB_NONE = -1;
+  const FUNC_LIB_SHARED = -2;
+  const libForFunc = new Int32Array(funcTable.length).fill(FUNC_LIB_NONE);
+  const framesByLib = new Map<
+    IndexIntoLibs,
+    { frames: IndexIntoFrameTable[]; addresses: Address[] }
+  >();
+  for (let frameIndex = 0; frameIndex < frameTable.length; frameIndex++) {
+    const libIndex = frameTable.lib[frameIndex];
+    if (libIndex === -1) {
       continue;
     }
-    const libIndex = resourceTable.lib[resourceIndex];
-    if (libIndex === null) {
-      // We can get here if we have pre-symbolicated "funcName (in LibraryName)"
-      // frames. Those get ResourceType.Library but no libIndex.
-      continue;
+    let entry = framesByLib.get(libIndex);
+    if (entry === undefined) {
+      entry = { frames: [], addresses: [] };
+      framesByLib.set(libIndex, entry);
     }
-    const lib = libs[libIndex];
-    if (lib === undefined) {
-      throw new Error('Did not find a lib.');
+    entry.frames.push(frameIndex);
+    entry.addresses.push(frameTable.address[frameIndex]);
+
+    const funcIndex = frameTable.func[frameIndex];
+    const knownLib = libForFunc[funcIndex];
+    if (knownLib === FUNC_LIB_NONE) {
+      libForFunc[funcIndex] = libIndex;
+    } else if (knownLib !== libIndex) {
+      libForFunc[funcIndex] = FUNC_LIB_SHARED;
     }
+  }
 
-    // Collect the set of funcs for this library in this thread.
-    const allFuncsForThisLib = new Set<IndexIntoFuncTable>();
-    for (let funcIndex = 0; funcIndex < funcTable.length; funcIndex++) {
-      if (funcTable.resource[funcIndex] !== resourceIndex) {
-        continue;
+  // Pass over the funcs: assign each func to the library that gets to recycle
+  // it, and remember one resource per library for the funcs we create later.
+  const funcsByLib = new Map<IndexIntoLibs, Set<IndexIntoFuncTable>>();
+  const resourceForLib = new Map<IndexIntoLibs, IndexIntoResourceTable>();
+  for (let funcIndex = 0; funcIndex < funcTable.length; funcIndex++) {
+    const libIndex = libForFunc[funcIndex];
+    if (libIndex < 0) {
+      continue;
+    }
+    let funcs = funcsByLib.get(libIndex);
+    if (funcs === undefined) {
+      funcs = new Set();
+      funcsByLib.set(libIndex, funcs);
+    }
+    funcs.add(funcIndex);
+    if (!resourceForLib.has(libIndex)) {
+      const resourceIndex = funcTable.resource[funcIndex];
+      if (resourceIndex !== -1) {
+        resourceForLib.set(libIndex, resourceIndex);
       }
-      allFuncsForThisLib.add(funcIndex);
     }
+  }
 
-    // Collect the set of native symbols for this library in this thread.
-    const allNativeSymbolsForThisLib: Set<IndexIntoNativeSymbolTable> =
-      new Set();
-    for (
-      let nativeSymbolIndex = 0;
-      nativeSymbolIndex < nativeSymbols.length;
-      nativeSymbolIndex++
-    ) {
-      if (nativeSymbols.libIndex[nativeSymbolIndex] !== libIndex) {
-        continue;
-      }
-      allNativeSymbolsForThisLib.add(nativeSymbolIndex);
+  // Pass over the native symbols: group them by library.
+  const nativeSymbolsByLib = new Map<
+    IndexIntoLibs,
+    Set<IndexIntoNativeSymbolTable>
+  >();
+  for (
+    let nativeSymbolIndex = 0;
+    nativeSymbolIndex < nativeSymbols.length;
+    nativeSymbolIndex++
+  ) {
+    const libIndex = nativeSymbols.libIndex[nativeSymbolIndex];
+    let symbols = nativeSymbolsByLib.get(libIndex);
+    if (symbols === undefined) {
+      symbols = new Set();
+      nativeSymbolsByLib.set(libIndex, symbols);
     }
+    symbols.add(nativeSymbolIndex);
+  }
 
-    // Collect the sets of frames and addresses for this library.
-    const allFramesForThisLib = [];
-    const frameAddresses = [];
-    for (let frameIndex = 0; frameIndex < frameTable.length; frameIndex++) {
-      const funcIndex = frameTable.func[frameIndex];
-      if (funcTable.resource[funcIndex] !== resourceIndex) {
-        continue;
-      }
-      allFramesForThisLib.push(frameIndex);
-      frameAddresses.push(frameTable.address[frameIndex]);
+  const map = new Map<string, ProfileLibSymbolicationInfo>();
+  for (const [libIndex, { frames, addresses }] of framesByLib) {
+    const lib = libs[libIndex];
+    if (lib === undefined) {
+      throw new Error('Did not find a lib.');
     }
 
     const libKey = `${lib.debugName}/${lib.breakpadId}`;
     map.set(libKey, {
       libIndex,
-      resourceIndex,
-      allFuncsForThisLib,
-      allNativeSymbolsForThisLib,
-      allFramesForThisLib,
-      frameAddresses,
+      resourceIndex: resourceForLib.get(libIndex) ?? -1,
+      allFuncsForThisLib: funcsByLib.get(libIndex) ?? new Set(),
+      allNativeSymbolsForThisLib: nativeSymbolsByLib.get(libIndex) ?? new Set(),
+      allFramesForThisLib: frames,
+      frameAddresses: addresses,
     });
   }
   return map;
@@ -903,6 +936,7 @@ function _partiallyApplySymbolicationStep(
         frameTable.subcategory[expansionFrameIndex] = subcategory;
         frameTable.innerWindowID[expansionFrameIndex] = innerWindowID;
         frameTable.address[expansionFrameIndex] = address;
+        frameTable.lib[expansionFrameIndex] = libIndex;
         frameTable.nativeSymbol[expansionFrameIndex] = nativeSymbolIndex;
         frameTable.originalLocation[expansionFrameIndex] = null;
 
diff --git a/src/profile-query/formatters/call-tree.ts b/src/profile-query/formatters/call-tree.ts
index 5113b81607..fb3a96b26b 100644
--- a/src/profile-query/formatters/call-tree.ts
+++ b/src/profile-query/formatters/call-tree.ts
@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 import type { CallTree } from 'firefox-profiler/profile-logic/call-tree';
-import type { IndexIntoCallNodeTable, Lib } from 'firefox-profiler/types';
+import type { IndexIntoCallNodeTable } from 'firefox-profiler/types';
 import { assertExhaustiveCheck } from 'firefox-profiler/utils/types';
 import type {
   CallTreeNode,
@@ -172,7 +172,6 @@ export type CallTreeCollectionOptions = {
  */
 export function collectCallTree(
   tree: CallTree,
-  libs: Lib[],
   options: CallTreeCollectionOptions = {}
 ): CallTreeNode {
   const maxNodes = options.maxNodes ?? 100;
@@ -244,7 +243,7 @@ export function collectCallTree(
     }
   }
 
-  return buildTreeStructure(tree, includedNodes, libs);
+  return buildTreeStructure(tree, includedNodes);
 }
 
 /**
@@ -252,8 +251,7 @@ export function collectCallTree(
  */
 function buildTreeStructure(
   tree: CallTree,
-  includedNodes: Set<IndexIntoCallNodeTable>,
-  libs: Lib[]
+  includedNodes: Set<IndexIntoCallNodeTable>
 ): CallTreeNode {
   // Get total sample count from the tree for percentage calculations
   const totalSampleCount = tree.getTotal();
@@ -299,8 +297,7 @@ function buildTreeStructure(
       // Format function name with library prefix
       const nameWithLibrary = formatFunctionNameWithLibrary(
         funcIndex,
-        tree._thread,
-        libs
+        tree._thread
       );
 
       const inlineStatus = inlineStatusForNode(tree, callNodeIndex);
diff --git a/src/profile-query/formatters/marker-info.ts b/src/profile-query/formatters/marker-info.ts
index 3efbc9ddef..f671c78a34 100644
--- a/src/profile-query/formatters/marker-info.ts
+++ b/src/profile-query/formatters/marker-info.ts
@@ -951,8 +951,7 @@ function collectStackTrace(
     return null;
   }
 
-  const { stackTable, frameTable, funcTable, stringTable, resourceTable } =
-    thread;
+  const { stackTable, frameTable, funcTable, stringTable } = thread;
   const frames: StackTraceData['frames'] = [];
 
   let currentStackIndex: IndexIntoStackTable = stackIndex;
@@ -960,19 +959,12 @@ function collectStackTrace(
     const frameIndex = stackTable.frame[currentStackIndex];
     const funcIndex = frameTable.func[frameIndex];
     const funcName = stringTable.getString(funcTable.name[funcIndex]);
-    const nameWithLibrary = formatFunctionNameWithLibrary(
-      funcIndex,
-      thread,
-      libs
-    );
+    const nameWithLibrary = formatFunctionNameWithLibrary(funcIndex, thread);
 
     let library: string | undefined;
-    const resourceIndex = funcTable.resource[funcIndex];
-    if (resourceIndex !== -1) {
-      const libIndex = resourceTable.lib[resourceIndex];
-      if (libIndex !== null && libs) {
-        library = libs[libIndex].name;
-      }
+    const libIndex = frameTable.lib[frameIndex];
+    if (libIndex !== -1 && libs) {
+      library = libs[libIndex].name;
     }
 
     frames.push({ name: funcName, nameWithLibrary, library });
diff --git a/src/profile-query/formatters/thread-info.ts b/src/profile-query/formatters/thread-info.ts
index 96095e4ffc..4495d45eaf 100644
--- a/src/profile-query/formatters/thread-info.ts
+++ b/src/profile-query/formatters/thread-info.ts
@@ -9,7 +9,6 @@ import {
 import {
   getCategories,
   getDefaultCategory,
-  getProfile,
 } from 'firefox-profiler/selectors/profile';
 import { collectSliceTree } from '../cpu-activity';
 import { computeThreadNetworkSummary } from '../network-summary';
@@ -114,14 +113,13 @@ export function collectThreadSamples(
   const threadSelectors = getThreadSelectors(threadIndexes);
   const friendlyThreadName = threadSelectors.getFriendlyThreadName(state);
   const thread = threadSelectors.getFilteredThread(state);
-  const libs = getProfile(state).libs;
 
   // Get call trees for analysis
   const functionListTree = threadSelectors.getFunctionListTree(state);
   const callTree = threadSelectors.getCallTree(state);
 
   // Extract function data
-  const functions = extractFunctionData(functionListTree, thread, libs);
+  const functions = extractFunctionData(functionListTree, thread);
 
   // Sort by total and take top 50
   const sortedByTotal = functions
@@ -201,11 +199,7 @@ export function collectThreadSamples(
 
         let hasInlinedFrames = false;
         const frames = heaviestPath.map((funcIndex, depth) => {
-          const funcName = formatFunctionNameWithLibrary(
-            funcIndex,
-            thread,
-            libs
-          );
+          const funcName = formatFunctionNameWithLibrary(funcIndex, thread);
           const funcData = funcMap.get(funcIndex);
           const prefixPath = heaviestPath.slice(0, depth + 1);
           const frameCallNodeIndex =
@@ -307,8 +301,7 @@ export function collectThreadSamplesBottomUp(
     weightType
   );
 
-  const libs = getProfile(state).libs;
-  const invertedCallTree = collectCallTree(invertedTree, libs, callTreeOptions);
+  const invertedCallTree = collectCallTree(invertedTree, callTreeOptions);
 
   return {
     type: 'thread-samples-bottom-up',
@@ -337,10 +330,9 @@ export function collectThreadSamplesTopDown(
   const threadSelectors = getThreadSelectors(threadIndexes);
   const friendlyThreadName = threadSelectors.getFriendlyThreadName(state);
   const callTree = threadSelectors.getCallTree(state);
-  const libs = getProfile(state).libs;
 
   // Collect regular call tree
-  const regularCallTree = collectCallTree(callTree, libs, callTreeOptions);
+  const regularCallTree = collectCallTree(callTree, callTreeOptions);
 
   return {
     type: 'thread-samples-top-down',
@@ -369,13 +361,12 @@ export function collectThreadFunctions(
   const threadSelectors = getThreadSelectors(threadIndexes);
   const friendlyThreadName = threadSelectors.getFriendlyThreadName(state);
   const thread = threadSelectors.getFilteredThread(state);
-  const libs = getProfile(state).libs;
 
   // Get function list tree
   const functionListTree = threadSelectors.getFunctionListTree(state);
 
   // Extract function data
-  const allFunctions = extractFunctionData(functionListTree, thread, libs);
+  const allFunctions = extractFunctionData(functionListTree, thread);
   const totalFunctionCount = allFunctions.length;
 
   // Check if we're zoomed (have committed ranges)
diff --git a/src/profile-query/function-annotate.ts b/src/profile-query/function-annotate.ts
index 20c86a4444..715e18a22b 100644
--- a/src/profile-query/function-annotate.ts
+++ b/src/profile-query/function-annotate.ts
@@ -6,7 +6,7 @@ import { getProfile } from 'firefox-profiler/selectors/profile';
 import { getSelectedThreadIndexes } from 'firefox-profiler/selectors/url-state';
 import { getThreadSelectors } from 'firefox-profiler/selectors/per-thread';
 import { parseFunctionHandle } from './function-map';
-import { getLibForFunc } from './function-list';
+import { getLibNameForFunc } from './function-list';
 import type { ThreadMap } from './thread-map';
 import {
   getStackLineInfo,
@@ -343,12 +343,12 @@ export async function functionAnnotate(
   const funcIndex = parseFunctionHandle(functionHandle, funcTable.length);
   const funcName = stringArray[funcTable.name[funcIndex]];
 
-  const libraryName = getLibForFunc(
+  const libraryName = getLibNameForFunc(
     funcIndex,
     funcTable,
     resourceTable,
-    profile.libs
-  )?.name;
+    stringArray
+  );
   const fullName = libraryName ? `${libraryName}!${funcName}` : funcName;
 
   const threadIndexes = getSelectedThreadIndexes(state);
diff --git a/src/profile-query/function-list.ts b/src/profile-query/function-list.ts
index ebb5edca97..b1ef369411 100644
--- a/src/profile-query/function-list.ts
+++ b/src/profile-query/function-list.ts
@@ -5,31 +5,58 @@
 import type {
   Thread,
   Lib,
+  RawFrameTable,
   FuncTable,
   ResourceTable,
 } from 'firefox-profiler/types';
+import { ResourceType } from 'firefox-profiler/types';
 import { getFunctionHandle } from './function-map';
 
 /**
  * Look up the Lib record for a function, or undefined if none is associated.
+ *
+ * For funcs which are shared across frames from multiple different libs, this
+ * will return the first match.
  */
-export function getLibForFunc(
+export function getAnyLibForFunc(
   funcIndex: number,
-  funcTable: FuncTable,
-  resourceTable: ResourceTable,
+  frameTable: RawFrameTable,
   libs: Lib[]
 ): Lib | undefined {
-  const resourceIndex = funcTable.resource[funcIndex];
-  if (resourceIndex === -1) {
-    return undefined;
-  }
-  const libIndex = resourceTable.lib[resourceIndex];
-  if (libIndex !== null && libIndex !== undefined && libIndex >= 0) {
-    return libs[libIndex];
+  for (let frameIndex = 0; frameIndex < frameTable.length; frameIndex++) {
+    if (frameTable.func[frameIndex] !== funcIndex) {
+      continue;
+    }
+    const libIndex = frameTable.lib[frameIndex];
+    if (libIndex !== -1) {
+      return libs[libIndex];
+    }
   }
   return undefined;
 }
 
+/**
+ * Look up the name of the library a function came from, or null if the function
+ * isn't native code. This is the name of the func's resource, which is cheap to
+ * get at; note that it names the library but does not identify a specific
+ * build, since several libs can share one resource.
+ */
+export function getLibNameForFunc(
+  funcIndex: number,
+  funcTable: FuncTable,
+  resourceTable: ResourceTable,
+  stringArray: string[]
+): string | null {
+  const resourceIndex = funcTable.resource[funcIndex];
+  if (
+    resourceIndex === -1 ||
+    resourceTable.type[resourceIndex] !== ResourceType.Library
+  ) {
+    return null;
+  }
+  return stringArray[resourceTable.name[resourceIndex]];
+}
+
 export type FunctionData = {
   funcName: string;
   funcIndex: number;
@@ -351,22 +378,13 @@ export function truncateFunctionName(
  */
 export function formatFunctionNameWithLibrary(
   funcIndex: number,
-  thread: Thread,
-  libs: Lib[]
+  thread: Thread
 ): string {
   const funcName = thread.stringTable.getString(
     thread.funcTable.name[funcIndex]
   );
-  const lib = getLibForFunc(
-    funcIndex,
-    thread.funcTable,
-    thread.resourceTable,
-    libs
-  );
-  if (lib) {
-    return `${lib.name}!${funcName}`;
-  }
-  // Fall back to resource name if no library
+  // The func's resource carries the library name for native code, and the
+  // origin / URL for JS code.
   const resourceIndex = thread.funcTable.resource[funcIndex];
   if (resourceIndex !== -1) {
     const resourceName = thread.stringTable.getString(
@@ -393,18 +411,13 @@ export function extractFunctionData(
       selfRelative: number;
     };
   },
-  thread: Thread,
-  libs: Lib[]
+  thread: Thread
 ): FunctionData[] {
   const roots = tree.getRoots();
   return roots.map((nodeIndex) => {
     const data = tree.getNodeData(nodeIndex);
     // The node index IS the function index for function list trees
-    const formattedName = formatFunctionNameWithLibrary(
-      nodeIndex,
-      thread,
-      libs
-    );
+    const formattedName = formatFunctionNameWithLibrary(nodeIndex, thread);
     return {
       ...data,
       funcName: formattedName,
diff --git a/src/profile-query/index.ts b/src/profile-query/index.ts
index 11d58a0cf8..c752ee4c74 100644
--- a/src/profile-query/index.ts
+++ b/src/profile-query/index.ts
@@ -61,7 +61,7 @@ import {
   type EligibleSource,
 } from 'firefox-profiler/profile-logic/source-map-matching';
 import { assertExhaustiveCheck } from 'firefox-profiler/utils/types';
-import { getLibForFunc } from './function-list';
+import { getAnyLibForFunc, getLibNameForFunc } from './function-list';
 import { MarkerMap } from './marker-map';
 import { loadProfileFromFileOrUrl, type LoadOptions } from './loader';
 import { collectProfileInfo } from './formatters/profile-info';
@@ -1110,12 +1110,9 @@ export class ProfileQuerier {
     // Look up the function
     const funcIndex = parseFunctionHandle(functionHandle, funcTable.length);
     const funcName = stringArray[funcTable.name[funcIndex]];
-    const library = getLibForFunc(
-      funcIndex,
-      funcTable,
-      resourceTable,
-      profile.libs
-    )?.name;
+    const library =
+      getLibNameForFunc(funcIndex, funcTable, resourceTable, stringArray) ??
+      undefined;
     const fullName = library ? `${library}!${funcName}` : funcName;
 
     return {
@@ -1156,10 +1153,9 @@ export class ProfileQuerier {
       };
     }
 
-    const lib = getLibForFunc(
+    const lib = getAnyLibForFunc(
       funcIndex,
-      funcTable,
-      resourceTable,
+      profile.shared.frameTable,
       profile.libs
     );
     if (lib) {
diff --git a/src/profile-query/types.ts b/src/profile-query/types.ts
index 5f3dc6cc2d..feb0d83dc8 100644
--- a/src/profile-query/types.ts
+++ b/src/profile-query/types.ts
@@ -184,6 +184,11 @@ export type FunctionInfoResult = {
     name: string;
     index: number;
   };
+  // The library of this function, if any.
+  // Note that, these days, funcs can be associated with multiple
+  // libraries, so this isn't the best representation anymore. In those
+  // cases this will be set to one of them, but it's arbitrary which one.
+  // See https://github.com/firefox-devtools/profiler/issues/6270
   library?: {
     name: string;
     path: string;
diff --git a/src/reducers/url-state.ts b/src/reducers/url-state.ts
index 0c8a92be9a..5374e6440f 100644
--- a/src/reducers/url-state.ts
+++ b/src/reducers/url-state.ts
@@ -628,7 +628,6 @@ const profileName: Reducer<string | null> = (state = null, action) => {
 const sourceView: Reducer<SourceViewState> = (
   state = {
     scrollGeneration: 0,
-    libIndex: null,
     sourceIndex: null,
     highlightedLine: null,
   },
@@ -641,7 +640,6 @@ const sourceView: Reducer<SourceViewState> = (
         scrollGeneration: shouldScroll
           ? state.scrollGeneration + 1
           : state.scrollGeneration,
-        libIndex: action.libIndex,
         sourceIndex: action.sourceIndex,
         scrollToLineNumber: action.scrollToLineNumber,
         highlightedLine: action.highlightedLineNumber,
diff --git a/src/test/fixtures/profiles/call-nodes.ts b/src/test/fixtures/profiles/call-nodes.ts
index 8692daf1ab..9f35027858 100644
--- a/src/test/fixtures/profiles/call-nodes.ts
+++ b/src/test/fixtures/profiles/call-nodes.ts
@@ -78,6 +78,7 @@ export default function getProfile(): Profile {
     func: frameFuncs.map((stringIndex) => funcTable.name.indexOf(stringIndex)),
     address: Array(frameFuncs.length).fill(-1),
     inlineDepth: Array(frameFuncs.length).fill(0),
+    lib: Array(frameFuncs.length).fill(-1),
     nativeSymbol: Array(frameFuncs.length).fill(null),
     category: Array(frameFuncs.length).fill(null),
     subcategory: Array(frameFuncs.length).fill(null),
diff --git a/src/test/fixtures/profiles/processed-profile.ts b/src/test/fixtures/profiles/processed-profile.ts
index dc886ee205..a765bef123 100644
--- a/src/test/fixtures/profiles/processed-profile.ts
+++ b/src/test/fixtures/profiles/processed-profile.ts
@@ -41,6 +41,7 @@ import type {
   Thread,
   ThreadIndex,
   IndexIntoCategoryList,
+  IndexIntoLibs,
   IndexIntoStackTable,
   CategoryList,
   JsTracerTable,
@@ -583,7 +584,7 @@ export type ProfileWithDicts = {
  *
  * The following func and frame attributes are supported:
  *  - [cat:*] - The category name, affects frameTable.category
- *  - [lib:*] - The library name, affects funcTable.resource + resourceTable + libs
+ *  - [lib:*] - The library name, affects frameTable.lib + funcTable.resource + resourceTable + libs
  *  - [file:*] - The filename, affects funcTable.file
  *  - [line:*] - The line, affects frameTable.line
  *  - [address:*] - The frame address, affects frameTable.address
@@ -600,8 +601,8 @@ function getFrame(
 ) {
   const funcIndex = frameTable.func[frameIndex];
   let s = stringTable.getString(funcTable.name[funcIndex]);
-  const libIndex = resourceTable.lib[funcTable.resource[funcIndex]];
-  if (libIndex !== null) {
+  const libIndex = frameTable.lib[frameIndex];
+  if (libIndex !== -1) {
     const libName = libs[libIndex].name;
     s += `[lib:${libName}]`;
   }
@@ -902,7 +903,7 @@ function _buildThreadFromTextOnlyStacks(
       // Find the library name from the function name and create an entry if needed.
       const libraryName = _findLibNameFromFuncName(funcNameWithModifier);
       let resourceIndex = -1;
-      let libIndex = null;
+      let libIndex: IndexIntoLibs | -1 = -1;
       if (libraryName !== null) {
         libIndex = globalDataCollector.indexForLib({
           arch: '',
@@ -913,7 +914,7 @@ function _buildThreadFromTextOnlyStacks(
           breakpadId: 'SOMETHING_FAKE',
           codeId: null,
         });
-        resourceIndex = globalDataCollector.indexForLibResource(libIndex);
+        resourceIndex = globalDataCollector.indexForLibResourceByLib(libIndex);
       }
 
       // Find the file name from the function name
@@ -947,7 +948,7 @@ function _buildThreadFromTextOnlyStacks(
       const nativeSymbolInfo =
         _findNativeSymbolNameFromFuncName(funcNameWithModifier);
       if (nativeSymbolInfo) {
-        if (libIndex === null) {
+        if (libIndex === -1) {
           throw new Error(
             `[sym:] has to be used together with [lib:] - missing lib in "${funcNameWithModifier}"`
           );
@@ -975,7 +976,8 @@ function _buildThreadFromTextOnlyStacks(
           lineNumber === frameTable.line[i] &&
           address === frameTable.address[i] &&
           inlineDepth === frameTable.inlineDepth[i] &&
-          nativeSymbol === frameTable.nativeSymbol[i]
+          nativeSymbol === frameTable.nativeSymbol[i] &&
+          libIndex === frameTable.lib[i]
         ) {
           frameIndex = i;
           break;
@@ -984,6 +986,7 @@ function _buildThreadFromTextOnlyStacks(
 
       if (frameIndex === undefined) {
         frameTable.func.push(funcIndex);
+        frameTable.lib.push(libIndex);
         frameTable.address.push(address);
         frameTable.inlineDepth.push(inlineDepth);
         frameTable.category.push(category);
@@ -2084,6 +2087,7 @@ export function addInnerWindowIdToStacks(
         frameTable.subcategory[foundFrameIndex]
       );
       frameTableBuilder.func.push(frameTable.func[foundFrameIndex]);
+      frameTableBuilder.lib.push(frameTable.lib[foundFrameIndex]);
       frameTableBuilder.nativeSymbol.push(
         frameTable.nativeSymbol[foundFrameIndex]
       );
diff --git a/src/test/integration/profiler-edit/__snapshots__/profiler-edit.test.ts.snap b/src/test/integration/profiler-edit/__snapshots__/profiler-edit.test.ts.snap
index 8df0ad49ac..4732177b42 100644
--- a/src/test/integration/profiler-edit/__snapshots__/profiler-edit.test.ts.snap
+++ b/src/test/integration/profiler-edit/__snapshots__/profiler-edit.test.ts.snap
@@ -87,7 +87,7 @@ Object {
     "markerSchema": Array [],
     "oscpu": "macOS 14.6.1",
     "pausedRanges": Array [],
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "a.out",
     "sampleUnits": Object {
@@ -370,6 +370,50 @@ Object {
         null,
       ],
       "length": 42,
+      "lib": Array [
+        0,
+        1,
+        2,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        2,
+        2,
+        5,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+      ],
       "line": Array [
         null,
         null,
@@ -743,14 +787,6 @@ Object {
         null,
       ],
       "length": 6,
-      "lib": Array [
-        0,
-        1,
-        2,
-        3,
-        4,
-        5,
-      ],
       "name": Array [
         0,
         1,
@@ -1452,7 +1488,7 @@ Object {
     "markerSchema": Array [],
     "oscpu": "macOS 14.6.1",
     "pausedRanges": Array [],
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "a.out",
     "sampleUnits": Object {
@@ -1735,6 +1771,50 @@ Object {
         null,
       ],
       "length": 42,
+      "lib": Array [
+        0,
+        1,
+        2,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        2,
+        2,
+        5,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+      ],
       "line": Array [
         null,
         null,
@@ -2108,14 +2188,6 @@ Object {
         null,
       ],
       "length": 6,
-      "lib": Array [
-        0,
-        1,
-        2,
-        3,
-        4,
-        5,
-      ],
       "name": Array [
         0,
         1,
@@ -2817,7 +2889,7 @@ Object {
     "markerSchema": Array [],
     "oscpu": "macOS 14.6.1",
     "pausedRanges": Array [],
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "a.out",
     "sampleUnits": Object {
@@ -3100,6 +3172,50 @@ Object {
         null,
       ],
       "length": 42,
+      "lib": Array [
+        0,
+        1,
+        2,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        2,
+        2,
+        5,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+      ],
       "line": Array [
         null,
         null,
@@ -3473,14 +3589,6 @@ Object {
         null,
       ],
       "length": 6,
-      "lib": Array [
-        0,
-        1,
-        2,
-        3,
-        4,
-        5,
-      ],
       "name": Array [
         0,
         1,
@@ -4182,7 +4290,7 @@ Object {
     "markerSchema": Array [],
     "oscpu": "macOS 14.6.1",
     "pausedRanges": Array [],
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "a.out",
     "sampleUnits": Object {
@@ -4465,6 +4573,50 @@ Object {
         null,
       ],
       "length": 42,
+      "lib": Array [
+        0,
+        1,
+        2,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+        2,
+        2,
+        2,
+        5,
+        2,
+        1,
+        1,
+        4,
+        4,
+        3,
+        1,
+      ],
       "line": Array [
         null,
         null,
@@ -4838,14 +4990,6 @@ Object {
         null,
       ],
       "length": 6,
-      "lib": Array [
-        0,
-        1,
-        2,
-        3,
-        4,
-        5,
-      ],
       "name": Array [
         0,
         1,
diff --git a/src/test/store/__snapshots__/profile-view.test.ts.snap b/src/test/store/__snapshots__/profile-view.test.ts.snap
index c16fdb16e5..2b7fc08e1a 100644
--- a/src/test/store/__snapshots__/profile-view.test.ts.snap
+++ b/src/test/store/__snapshots__/profile-view.test.ts.snap
@@ -428,7 +428,7 @@ Object {
     "oscpu": "",
     "physicalCPUs": 0,
     "platform": "",
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "Firefox",
     "sourceURL": "",
@@ -515,6 +515,17 @@ Object {
         0,
       ],
       "length": 9,
+      "lib": Int32Array [
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+      ],
       "line": Array [
         null,
         null,
@@ -661,7 +672,6 @@ Object {
     "resourceTable": Object {
       "host": Array [],
       "length": 0,
-      "lib": Array [],
       "name": Array [],
       "type": Array [],
     },
@@ -2486,6 +2496,17 @@ CallTree {
         0,
       ],
       "length": 9,
+      "lib": Int32Array [
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+      ],
       "line": Array [
         null,
         null,
@@ -2655,7 +2676,6 @@ CallTree {
     "resourceTable": Object {
       "host": Array [],
       "length": 0,
-      "lib": Array [],
       "name": Array [],
       "type": Array [],
     },
@@ -2874,6 +2894,17 @@ Object {
       0,
     ],
     "length": 9,
+    "lib": Int32Array [
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+    ],
     "line": Array [
       null,
       null,
@@ -3043,7 +3074,6 @@ Object {
   "resourceTable": Object {
     "host": Array [],
     "length": 0,
-    "lib": Array [],
     "name": Array [],
     "type": Array [],
   },
@@ -3342,6 +3372,17 @@ Object {
       0,
     ],
     "length": 9,
+    "lib": Int32Array [
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+    ],
     "line": Array [
       null,
       null,
@@ -3511,7 +3552,6 @@ Object {
   "resourceTable": Object {
     "host": Array [],
     "length": 0,
-    "lib": Array [],
     "name": Array [],
     "type": Array [],
   },
@@ -3716,6 +3756,17 @@ Object {
       0,
     ],
     "length": 9,
+    "lib": Int32Array [
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+    ],
     "line": Array [
       null,
       null,
@@ -3885,7 +3936,6 @@ Object {
   "resourceTable": Object {
     "host": Array [],
     "length": 0,
-    "lib": Array [],
     "name": Array [],
     "type": Array [],
   },
@@ -4102,6 +4152,17 @@ Object {
       0,
     ],
     "length": 9,
+    "lib": Int32Array [
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+      -1,
+    ],
     "line": Array [
       null,
       null,
@@ -4271,7 +4332,6 @@ Object {
   "resourceTable": Object {
     "host": Array [],
     "length": 0,
-    "lib": Array [],
     "name": Array [],
     "type": Array [],
   },
diff --git a/src/test/store/bottom-box.test.ts b/src/test/store/bottom-box.test.ts
index 32a6e1c1a4..64037f2faa 100644
--- a/src/test/store/bottom-box.test.ts
+++ b/src/test/store/bottom-box.test.ts
@@ -354,7 +354,6 @@ describe('bottom box', function () {
 
     dispatch(
       updateBottomBoxContentsAndMaybeOpen('calltree', {
-        libIndex: null,
         sourceIndex: null,
         nativeSymbols: [],
         initialNativeSymbol: 0,
diff --git a/src/test/store/symbolication.test.ts b/src/test/store/symbolication.test.ts
index 81771af3ea..352f32a2d8 100644
--- a/src/test/store/symbolication.test.ts
+++ b/src/test/store/symbolication.test.ts
@@ -620,7 +620,6 @@ function _createUnsymbolicatedProfile() {
 
   profile.shared.resourceTable = {
     length: 1,
-    lib: [libIndex],
     name: [stringTable.indexForString('example lib')],
     host: [stringTable.indexForString('example host')],
     type: [ResourceType.Library],
@@ -628,6 +627,9 @@ function _createUnsymbolicatedProfile() {
   for (let i = 0; i < profile.shared.funcTable.length; i++) {
     profile.shared.funcTable.resource[i] = 0;
   }
+  for (let i = 0; i < profile.shared.frameTable.length; i++) {
+    profile.shared.frameTable.lib[i] = libIndex;
+  }
 
   // Add a marker with a cause stack. We use the stack of the first sample.
   // This sample has 0x000a in its stack, which has an inlined function call,
diff --git a/src/test/unit/__snapshots__/process-profile.test.ts.snap b/src/test/unit/__snapshots__/process-profile.test.ts.snap
index 72c8a2406d..5f7b34f429 100644
--- a/src/test/unit/__snapshots__/process-profile.test.ts.snap
+++ b/src/test/unit/__snapshots__/process-profile.test.ts.snap
@@ -207,7 +207,7 @@ Array [
       "host": null,
       "isJS": false,
       "lib": undefined,
-      "libIndex": undefined,
+      "libIndex": null,
       "lineNumber": null,
       "resourceIndex": -1,
       "resourceName": null,
diff --git a/src/test/unit/__snapshots__/profile-conversion.test.ts.snap b/src/test/unit/__snapshots__/profile-conversion.test.ts.snap
index a3831da47a..907fa724ce 100644
--- a/src/test/unit/__snapshots__/profile-conversion.test.ts.snap
+++ b/src/test/unit/__snapshots__/profile-conversion.test.ts.snap
@@ -42,7 +42,7 @@ Object {
         "RefreshDriverTick",
         "Network",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "ART Trace (Android)",
       "symbolicated": true,
       "version": 36,
@@ -1022,7 +1022,7 @@ Object {
         "RefreshDriverTick",
         "Network",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "ART Trace (Android)",
       "symbolicated": true,
       "version": 36,
@@ -2305,7 +2305,7 @@ Object {
       "markerSchemaNames": Array [
         "EventDispatch",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Chrome Trace",
       "symbolicated": true,
       "version": 36,
@@ -2697,7 +2697,7 @@ Object {
       "markerSchemaNames": Array [
         "EventDispatch",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Chrome Trace",
       "symbolicated": true,
       "version": 36,
@@ -3086,7 +3086,7 @@ Object {
       "markerSchemaNames": Array [
         "EventDispatch",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Chrome Trace",
       "symbolicated": true,
       "version": 36,
@@ -3187,7 +3187,7 @@ Object {
       "markerSchemaNames": Array [
         "EventDispatch",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Chrome Trace",
       "symbolicated": true,
       "version": 36,
@@ -3540,7 +3540,7 @@ Object {
       "markerSchemaNames": Array [
         "EventDispatch",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Chrome Trace",
       "symbolicated": true,
       "version": 36,
@@ -3605,7 +3605,7 @@ Object {
       "markerSchemaNames": Array [
         "EventDispatch",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Chrome Trace",
       "symbolicated": true,
       "version": 36,
@@ -3759,7 +3759,7 @@ Object {
       "markerSchemaNames": Array [
         "EventDispatch",
       ],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Chrome Trace",
       "symbolicated": true,
       "version": 36,
@@ -3817,7 +3817,7 @@ Object {
       "importedFrom": undefined,
       "interval": 1,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Firefox",
       "symbolicated": true,
       "version": 36,
@@ -4207,7 +4207,7 @@ Object {
       "importedFrom": undefined,
       "interval": 1,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Firefox",
       "symbolicated": true,
       "version": 36,
@@ -4265,7 +4265,7 @@ Object {
       "importedFrom": undefined,
       "interval": 1,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Firefox",
       "symbolicated": true,
       "version": 36,
@@ -4323,7 +4323,7 @@ Object {
       "importedFrom": undefined,
       "interval": 1,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Firefox",
       "symbolicated": true,
       "version": 36,
@@ -4643,7 +4643,7 @@ Object {
       "importedFrom": "Simpleperf",
       "interval": 0,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "com.example.sampleapplication",
       "symbolicated": undefined,
       "version": 30,
@@ -5019,7 +5019,7 @@ Object {
       "importedFrom": "Simpleperf",
       "interval": 0,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "com.example.sampleapplication",
       "symbolicated": undefined,
       "version": 30,
@@ -5319,7 +5319,7 @@ Object {
       "importedFrom": "dhat",
       "interval": 1,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "target/debug/examples/work_log (dhat)",
       "symbolicated": true,
       "version": 36,
@@ -5452,7 +5452,7 @@ Object {
       "importedFrom": undefined,
       "interval": 1,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Flamegraph",
       "symbolicated": true,
       "version": 36,
@@ -5510,7 +5510,7 @@ Object {
       "importedFrom": undefined,
       "interval": 1,
       "markerSchemaNames": Array [],
-      "preprocessedProfileVersion": 69,
+      "preprocessedProfileVersion": 70,
       "product": "Flamegraph",
       "symbolicated": true,
       "version": 36,
diff --git a/src/test/unit/__snapshots__/profile-upgrading.test.ts.snap b/src/test/unit/__snapshots__/profile-upgrading.test.ts.snap
index 394eaa6d2e..07d2263740 100644
--- a/src/test/unit/__snapshots__/profile-upgrading.test.ts.snap
+++ b/src/test/unit/__snapshots__/profile-upgrading.test.ts.snap
@@ -40,7 +40,7 @@ Object {
     "oscpu": undefined,
     "physicalCPUs": undefined,
     "platform": undefined,
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "Firefox",
     "sampleUnits": undefined,
@@ -1287,6 +1287,210 @@ Object {
         0,
       ],
       "length": 202,
+      "lib": Int32Array [
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+        -1,
+      ],
       "line": Array [
         null,
         null,
@@ -2722,20 +2926,6 @@ Object {
         null,
       ],
       "length": 12,
-      "lib": Array [
-        null,
-        null,
-        null,
-        null,
-        null,
-        null,
-        null,
-        null,
-        null,
-        null,
-        null,
-        null,
-      ],
       "name": Array [
         2,
         5,
@@ -7644,7 +7834,7 @@ Object {
     "misc": "rv:48.0",
     "oscpu": "Intel Mac OS X 10.11",
     "platform": "Macintosh",
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "Firefox",
     "stackwalk": 1,
@@ -7793,6 +7983,29 @@ Object {
         0,
       ],
       "length": 21,
+      "lib": Array [
+        -1,
+        0,
+        0,
+        -1,
+        -1,
+        0,
+        0,
+        -1,
+        0,
+        0,
+        -1,
+        -1,
+        0,
+        0,
+        -1,
+        1,
+        1,
+        -1,
+        -1,
+        1,
+        1,
+      ],
       "line": Array [
         null,
         null,
@@ -7995,11 +8208,6 @@ Object {
         null,
       ],
       "length": 3,
-      "lib": Array [
-        0,
-        null,
-        1,
-      ],
       "name": Array [
         11,
         10,
@@ -9021,7 +9229,7 @@ Object {
     "misc": "rv:48.0",
     "oscpu": "Intel Mac OS X 10.11",
     "platform": "Macintosh",
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "Firefox",
     "stackwalk": 1,
@@ -9182,6 +9390,31 @@ Object {
         0,
       ],
       "length": 23,
+      "lib": Array [
+        -1,
+        0,
+        0,
+        -1,
+        -1,
+        0,
+        0,
+        -1,
+        0,
+        0,
+        -1,
+        -1,
+        0,
+        0,
+        -1,
+        1,
+        1,
+        -1,
+        -1,
+        -1,
+        -1,
+        1,
+        1,
+      ],
       "line": Array [
         null,
         null,
@@ -9408,11 +9641,6 @@ Object {
         null,
       ],
       "length": 3,
-      "lib": Array [
-        0,
-        null,
-        1,
-      ],
       "name": Array [
         12,
         11,
@@ -10566,7 +10794,7 @@ Object {
     "misc": "rv:48.0",
     "oscpu": "Intel Mac OS X 10.11",
     "platform": "Macintosh",
-    "preprocessedProfileVersion": 69,
+    "preprocessedProfileVersion": 70,
     "processType": 0,
     "product": "Firefox",
     "stackwalk": 1,
@@ -10753,6 +10981,31 @@ Object {
         0,
       ],
       "length": 23,
+      "lib": Array [
+        -1,
+        0,
+        0,
+        -1,
+        -1,
+        0,
+        0,
+        -1,
+        0,
+        0,
+        -1,
+        -1,
+        0,
+        0,
+        -1,
+        1,
+        1,
+        -1,
+        -1,
+        -1,
+        -1,
+        1,
+        1,
+      ],
       "line": Array [
         null,
         null,
@@ -10979,11 +11232,6 @@ Object {
         null,
       ],
       "length": 3,
-      "lib": Array [
-        0,
-        null,
-        1,
-      ],
       "name": Array [
         13,
         12,
diff --git a/src/test/unit/merge-compare.test.ts b/src/test/unit/merge-compare.test.ts
index c064168786..8dd75b0ea1 100644
--- a/src/test/unit/merge-compare.test.ts
+++ b/src/test/unit/merge-compare.test.ts
@@ -18,6 +18,7 @@ import { ensureExists } from 'firefox-profiler/utils/types';
 import { getTimeRangeIncludingAllThreads } from 'firefox-profiler/profile-logic/profile-data';
 import { StringTable } from '../../utils/string-table';
 import type { RawProfileSharedData, Profile } from 'firefox-profiler/types';
+import { ResourceType } from 'firefox-profiler/types';
 import { callTreeFromProfile, formatTree } from '../fixtures/utils';
 import { storeWithProfile } from '../fixtures/stores';
 import { addTransformToStack } from '../../actions/profile-view';
@@ -50,6 +51,7 @@ describe('mergeProfilesForDiffing function', function () {
     const mergedShared = mergedProfile.shared;
     const mergedResources = mergedShared.resourceTable;
     const mergedFunctions = mergedShared.funcTable;
+    const mergedFrames = mergedShared.frameTable;
     const stringArray = mergedShared.stringArray;
 
     expect(mergedLibs).toHaveLength(3);
@@ -59,9 +61,8 @@ describe('mergeProfilesForDiffing function', function () {
     // Now check that all functions are linked to the right resources.
     // We should have 2 A functions, linked to 2 different resources.
     // And we should have 1 B function, and 1 C function.
-    const libsForA = [];
-    const resourcesForA = [];
-    for (let funcIndex = 0; funcIndex < mergedFunctions.length; funcIndex++) {
+    for (let frameIndex = 0; frameIndex < mergedFrames.length; frameIndex++) {
+      const funcIndex = mergedFrames.func[frameIndex];
       const funcName = stringArray[mergedFunctions.name[funcIndex]];
       const resourceIndex = mergedFunctions.resource[funcIndex];
 
@@ -72,18 +73,17 @@ describe('mergeProfilesForDiffing function', function () {
         if (nameIndex >= 0) {
           resourceName = stringArray[nameIndex];
         }
-
-        const libIndex = mergedResources.lib[resourceIndex];
-        if (libIndex !== null && libIndex !== undefined && libIndex >= 0) {
-          libName = mergedLibs[libIndex].name;
-        }
+      }
+      const libIndex = mergedFrames.lib[frameIndex];
+      if (libIndex !== null) {
+        libName = mergedLibs[libIndex].name;
       }
 
       /* eslint-disable jest/no-conditional-expect */
       switch (funcName) {
         case 'A':
-          libsForA.push(libName);
-          resourcesForA.push(resourceName);
+          expect(libName).toBeOneOf(['libA', 'libB']);
+          expect(resourceName).toBeOneOf(['libA', 'libB']);
           break;
         case 'B':
           expect(libName).toBe('libA');
@@ -97,8 +97,46 @@ describe('mergeProfilesForDiffing function', function () {
       }
       /* eslint-enable */
     }
-    expect(libsForA).toEqual(['libA', 'libB']);
-    expect(resourcesForA).toEqual(['libA', 'libB']);
+  });
+
+  it('keeps two builds of the same library apart while sharing one resource', function () {
+    // This is the case that motivated moving the lib column off the
+    // resourceTable and onto the frameTable: comparing two builds of libxul.
+    // Both builds have the same name, so they share a single resource, but they
+    // have different breakpadIds and so must stay separate libs - symbols have
+    // to be looked up separately for each build.
+    const sampleProfileA = getProfileFromTextSamples('A[lib:libxul.so]');
+    const sampleProfileB = getProfileFromTextSamples('A[lib:libxul.so]');
+    sampleProfileB.profile.libs[0] = {
+      ...sampleProfileB.profile.libs[0],
+      breakpadId: 'A_DIFFERENT_BUILD',
+    };
+    const profileState = stateFromLocation({
+      pathname: '/public/fakehash1/',
+      search: '?thread=0&v=3',
+      hash: '',
+    });
+
+    const { profile: mergedProfile } = mergeProfilesForDiffing(
+      [sampleProfileA.profile, sampleProfileB.profile],
+      [profileState, profileState]
+    );
+    const { resourceTable, frameTable, stringArray } = mergedProfile.shared;
+
+    // The two builds have separate libs.
+    expect(mergedProfile.libs.map((lib) => lib.breakpadId)).toEqual([
+      'SOMETHING_FAKE',
+      'A_DIFFERENT_BUILD',
+    ]);
+
+    // But there's only one resource because both libs are called `libxul.so`.
+    const libraryResources = resourceTable.name
+      .filter((_name, i) => resourceTable.type[i] === ResourceType.Library)
+      .map((nameIndex) => stringArray[nameIndex]);
+    expect(libraryResources).toEqual(['libxul.so']);
+
+    // The frames still have different libs.
+    expect([...frameTable.lib]).toEqual([0, 1]);
   });
 
   it('should set interval of merged profile to minimum of all intervals', function () {
diff --git a/src/test/unit/process-profile.test.ts b/src/test/unit/process-profile.test.ts
index 945bfd78e6..12404111f8 100644
--- a/src/test/unit/process-profile.test.ts
+++ b/src/test/unit/process-profile.test.ts
@@ -110,14 +110,15 @@ describe('extract functions and resource from location strings', function () {
   globalDataCollector.addExtensionOrigins(extensions);
 
   it('extracts the information for all different types of locations', function () {
-    const { frameFuncs } = extractFuncsAndResourcesFromFrameLocations(
-      locationIndexes,
-      locationIndexes.map(() => false),
-      geckoThreadStringArray,
-      libs,
-      globalDataCollector,
-      getEmptySourceTable()
-    );
+    const { frameFuncs, frameLibs } =
+      extractFuncsAndResourcesFromFrameLocations(
+        locationIndexes,
+        locationIndexes.map(() => false),
+        geckoThreadStringArray,
+        libs,
+        globalDataCollector,
+        getEmptySourceTable()
+      );
 
     const {
       shared: { sources, funcTable, resourceTable },
@@ -139,15 +140,13 @@ describe('extract functions and resource from location strings', function () {
           fileNameIndex === null ? null : stringTable.getString(fileNameIndex);
         const lineNumber = funcTable.lineNumber[funcIndex];
         const columnNumber = funcTable.columnNumber[funcIndex];
-
-        let libIndex, resourceName, host, resourceType;
+        let resourceName, host, resourceType;
         if (resourceIndex === -1) {
           resourceName = null;
           host = null;
           resourceType = null;
         } else {
           const hostStringIndex = resourceTable.host[resourceIndex];
-          libIndex = resourceTable.lib[resourceIndex];
           resourceName = stringTable.getString(
             resourceTable.name[resourceIndex]
           );
@@ -157,10 +156,8 @@ describe('extract functions and resource from location strings', function () {
               : stringTable.getString(hostStringIndex);
           resourceType = resourceTable.type[resourceIndex];
         }
-        const lib =
-          libIndex === undefined || libIndex === null || libIndex === -1
-            ? undefined
-            : libs[libIndex];
+        const libIndex = frameLibs[locationIndex];
+        const lib = libIndex === null ? undefined : libs[libIndex];
 
         return [
           locationName,
diff --git a/src/test/unit/profile-query/call-tree.test.ts b/src/test/unit/profile-query/call-tree.test.ts
index 41dbbf43b1..7bf2b1d1c6 100644
--- a/src/test/unit/profile-query/call-tree.test.ts
+++ b/src/test/unit/profile-query/call-tree.test.ts
@@ -23,10 +23,9 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
       // Collect with budget of 3 nodes
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 3,
       });
 
@@ -47,10 +46,9 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
       // With small budget, should still include D (100% at depth 3)
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 4,
       });
 
@@ -75,10 +73,9 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
       // With budget of 4: should get A, B (50%), D (50%), C (50%)
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 4,
       });
 
@@ -99,10 +96,9 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
       // With budget of 2: A and B, should show C/D/E as elided
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 2,
       });
 
@@ -125,9 +121,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 4,
         scoringStrategy: 'exponential-0.9',
       });
@@ -149,9 +144,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 4,
         scoringStrategy: 'percentage-only',
       });
@@ -175,9 +169,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 10,
         scoringStrategy: 'exponential-0.9',
       });
@@ -203,10 +196,9 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
       // Small budget to force truncation
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 3,
       });
 
@@ -237,7 +229,6 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
       // First verify that A has many children
       const roots = callTree.getRoots();
@@ -246,7 +237,7 @@ describe('call-tree collection', function () {
       const aChildren = callTree.getChildren(aCallNode);
       expect(aChildren.length).toBe(16); // B through Q
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 5, // Small budget to ensure truncation
         maxChildrenPerNode: 10,
       });
@@ -272,9 +263,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 10,
       });
 
@@ -302,9 +292,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 8,
         scoringStrategy: 'exponential-0.9',
       });
@@ -331,9 +320,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 100,
         maxDepth: 20,
       });
@@ -354,10 +342,9 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
       // Budget that includes A and B, but not the other children
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 2,
       });
 
@@ -392,9 +379,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 2,
       });
 
@@ -422,9 +408,8 @@ describe('call-tree collection', function () {
       const state = store.getState();
       const threadSelectors = getThreadSelectors(0);
       const callTree = threadSelectors.getCallTree(state);
-      const libs = profile.libs;
 
-      const result = collectCallTree(callTree, libs, {
+      const result = collectCallTree(callTree, {
         maxNodes: 1000, // High budget
         maxDepth: 10, // But limited depth
       });
diff --git a/src/test/unit/profile-query/function-list.test.ts b/src/test/unit/profile-query/function-list.test.ts
index d6a736d7cf..0d6ed65b72 100644
--- a/src/test/unit/profile-query/function-list.test.ts
+++ b/src/test/unit/profile-query/function-list.test.ts
@@ -12,7 +12,6 @@ import {
   type FunctionData,
 } from '../../../profile-query/function-list';
 import { getProfileFromTextSamples } from '../../fixtures/profiles/processed-profile';
-import type { Lib } from 'firefox-profiler/types';
 
 function createMockTree(functions: FunctionData[]) {
   return {
@@ -24,12 +23,11 @@ function createMockTree(functions: FunctionData[]) {
 describe('function-list', function () {
   describe('extractFunctionData', function () {
     it('extracts function data from a tree', function () {
-      const { profile, derivedThreads } = getProfileFromTextSamples(`
+      const { derivedThreads } = getProfileFromTextSamples(`
         foo
         bar
       `);
       const [thread] = derivedThreads;
-      const libs: Lib[] = profile.libs;
 
       const functions: FunctionData[] = [
         {
@@ -51,7 +49,7 @@ describe('function-list', function () {
       ];
 
       const tree = createMockTree(functions);
-      const result = extractFunctionData(tree, thread, libs);
+      const result = extractFunctionData(tree, thread);
 
       expect(result).toEqual(functions);
     });
diff --git a/src/test/unit/profile-tree.test.ts b/src/test/unit/profile-tree.test.ts
index 90f8a59a91..64fbc98f44 100644
--- a/src/test/unit/profile-tree.test.ts
+++ b/src/test/unit/profile-tree.test.ts
@@ -697,7 +697,6 @@ describe('origin annotation', function () {
     shared.funcTable.source[funcIndex] = location
       ? addSourceToTable(shared.sources, stringTable.indexForString(location))
       : null;
-    shared.resourceTable.lib.push(-1);
     shared.resourceTable.name.push(stringTable.indexForString(name));
     shared.resourceTable.host.push(
       host ? stringTable.indexForString(host) : null
diff --git a/src/test/unit/sanitize.test.ts b/src/test/unit/sanitize.test.ts
index 8ab505fbcc..720a290a39 100644
--- a/src/test/unit/sanitize.test.ts
+++ b/src/test/unit/sanitize.test.ts
@@ -1660,6 +1660,30 @@ describe('sanitizePII', function () {
     );
   });
 
+  it('should compact the libs and translate the frameTable lib column', function () {
+    // Thread 0's frames are in libA, thread 1's are in libB, and thread 2's
+    // frames have no library at all (lib === -1).
+    const { profile } = getProfileFromTextSamples(
+      `A[lib:libA.so]`,
+      `B[lib:libB.so]`,
+      `Cjs`
+    );
+
+    expect(profile.libs.map((lib) => lib.name)).toEqual(['libA.so', 'libB.so']);
+    expect([...profile.shared.frameTable.lib]).toEqual([0, 1, -1]);
+
+    // Remove thread 0, which is the only user of libA.so.
+    const { sanitizedProfile } = setup(
+      { shouldRemoveThreads: new Set([0]) },
+      profile
+    );
+
+    // libA.so is gone, and the surviving frames point at the reindexed libB.so
+    // while the lib-less frame keeps its -1 sentinel.
+    expect(sanitizedProfile.libs.map((lib) => lib.name)).toEqual(['libB.so']);
+    expect([...sanitizedProfile.shared.frameTable.lib]).toEqual([0, -1]);
+  });
+
   it('always removes source contents even when no PII removal is requested', function () {
     const { profile } = getProfileFromTextSamples(`A[file:file1.js]`);
     // There should be only one source.
diff --git a/src/test/url-handling.test.ts b/src/test/url-handling.test.ts
index 8855e4094f..c3f5919768 100644
--- a/src/test/url-handling.test.ts
+++ b/src/test/url-handling.test.ts
@@ -2030,7 +2030,6 @@ describe('URL persistence of bottom box (source view and assembly view)', functi
       'hg:hg.mozilla.org/mozilla-central:xpcom/threads/nsThread.cpp:5bb3e281dc9ec8a619c781d52882adb1cacf20bb';
     const sourceIndex = getSourceIndex(sourceFile);
     const bottomBoxInfo: BottomBoxInfo = {
-      libIndex: 0,
       sourceIndex,
       nativeSymbols: [],
       initialNativeSymbol: null,
@@ -2065,7 +2064,6 @@ describe('URL persistence of bottom box (source view and assembly view)', functi
       'hg:hg.mozilla.org/mozilla-central:xpcom/threads/nsThread.cpp:5bb3e281dc9ec8a619c781d52882adb1cacf20bb';
     const sourceIndex = getSourceIndex(sourceFile);
     const bottomBoxInfo: BottomBoxInfo = {
-      libIndex: 0,
       sourceIndex,
       nativeSymbols: [],
       initialNativeSymbol: null,
@@ -2096,7 +2094,6 @@ describe('URL persistence of bottom box (source view and assembly view)', functi
       functionSizeIsKnown: false,
     };
     const bottomBoxInfo: BottomBoxInfo = {
-      libIndex: 0,
       sourceIndex: null,
       nativeSymbols: [nativeSymbolInfo],
       initialNativeSymbol: 0,
@@ -2141,7 +2138,6 @@ describe('URL persistence of bottom box (source view and assembly view)', functi
       functionSizeIsKnown: false,
     };
     const bottomBoxInfo: BottomBoxInfo = {
-      libIndex: 0,
       sourceIndex,
       nativeSymbols: [nativeSymbolInfo],
       initialNativeSymbol: 0,
diff --git a/src/types/actions.ts b/src/types/actions.ts
index 7bff525522..888a3b05a9 100644
--- a/src/types/actions.ts
+++ b/src/types/actions.ts
@@ -11,7 +11,6 @@ import type {
   Pid,
   TabID,
   IndexIntoCategoryList,
-  IndexIntoLibs,
   PageList,
   IndexIntoSourceTable,
   FuncTable,
@@ -347,7 +346,6 @@ type ProfileAction =
     }
   | {
       readonly type: 'UPDATE_BOTTOM_BOX';
-      readonly libIndex: IndexIntoLibs | null;
       readonly sourceIndex: IndexIntoSourceTable | null;
       readonly nativeSymbols: NativeSymbolInfo[];
       readonly currentNativeSymbol: number | null;
diff --git a/src/types/profile-derived.ts b/src/types/profile-derived.ts
index 4da76d2ba1..d21f63645c 100644
--- a/src/types/profile-derived.ts
+++ b/src/types/profile-derived.ts
@@ -287,10 +287,10 @@ export type StackTable = {
  *
  * Differs from `RawFrameTable` in that the following columns are always
  * stored as typed arrays: `address` (`Int32Array`, with `-1` as the sentinel
- * for missing addresses), `inlineDepth` (`Uint8Array`), and `func`
- * (`Int32Array`). In `RawFrameTable`, these columns may be either regular
- * arrays or typed arrays, since regular arrays are convenient during
- * construction.
+ * for missing addresses), `inlineDepth` (`Uint8Array`), `func` (`Int32Array`),
+ * and `lib` (`Int32Array`, with `-1` as the sentinel for frames with no
+ * library). In `RawFrameTable`, these columns may be either regular arrays or
+ * typed arrays, since regular arrays are convenient during construction.
  */
 export type FrameTable = {
   // Differs from RawFrameTable: always Int32Array (-1 sentinel preserved).
@@ -301,6 +301,8 @@ export type FrameTable = {
   subcategory: (IndexIntoSubcategoryListForCategory | null)[];
   // Differs from RawFrameTable: always Int32Array.
   func: Int32Array<ArrayBuffer>;
+  // Differs from RawFrameTable: always Int32Array (-1 sentinel preserved).
+  lib: Int32Array<ArrayBuffer>;
   nativeSymbol: (IndexIntoNativeSymbolTable | null)[];
   innerWindowID: (InnerWindowID | null)[];
   line: (number | null)[];
@@ -861,7 +863,6 @@ export type NativeSymbolInfo = {
  * assembly view) is updated.
  */
 export type BottomBoxInfo = {
-  libIndex: IndexIntoLibs | null;
   sourceIndex: IndexIntoSourceTable | null;
   nativeSymbols: NativeSymbolInfo[];
   initialNativeSymbol: number | null; // index into `nativeSymbols`
diff --git a/src/types/profile.ts b/src/types/profile.ts
index a473c58223..debe76dba3 100644
--- a/src/types/profile.ts
+++ b/src/types/profile.ts
@@ -240,7 +240,7 @@ export type RawMarkerTable = {
  */
 export type RawFrameTable = {
   // If this is a frame for native code, the address is the address of the frame's
-  // assembly instruction,  relative to the native library that contains it.
+  // assembly instruction,  relative to the native library given by `lib`.
   //
   // For frames obtained from stack walking, the address points into the call instruction.
   // It is not a return address, it is a "nudged" return address (i.e. return address
@@ -248,12 +248,14 @@ export type RawFrameTable = {
   // is performed at the end of profile processing. See the big comment above
   // nudgeReturnAddresses for more details.
   //
-  // The library which this address is relative to is given by the frame's nativeSymbol:
-  // frame -> nativeSymbol -> lib.
-  //
   // Frames with no address use the sentinel value `-1`.
   address: Array<Address | -1> | Int32Array<ArrayBuffer>;
 
+  // The native library that this frame's code is in. Frames which aren't native
+  // code (JS frames, label frames), or whose library is unknown, use the
+  // sentinel value `-1`.
+  lib: Array<IndexIntoLibs | -1> | Int32Array<ArrayBuffer>;
+
   // The inline depth for this frame. If there is an inline stack at an address,
   // we create multiple frames with the same address, one for each depth.
   // The outermost frame always has depth 0.
@@ -408,12 +410,12 @@ export const enum ResourceType {
 }
 
 /**
- * The ResourceTable holds additional information about functions. It tends to contain
- * sparse arrays. Multiple functions can point to the same resource.
+ * "Resources" are groupings of functions - for example, these functions came
+ * from JS code from add-on X, or from JS files hosted at a certain origin,
+ * or from a native library with some name.
  */
 export type ResourceTable = {
   length: number;
-  lib: Array<IndexIntoLibs | null>;
   name: Array<IndexIntoStringTable>;
   host: Array<IndexIntoStringTable | null>;
   type: ResourceType[];
diff --git a/src/types/state.ts b/src/types/state.ts
index f5198e2a7f..5583e72181 100644
--- a/src/types/state.ts
+++ b/src/types/state.ts
@@ -22,7 +22,6 @@ import type {
   ThreadIndex,
   Pid,
   TabID,
-  IndexIntoLibs,
   IndexIntoSourceTable,
 } from './profile';
 
@@ -260,13 +259,6 @@ export type SourceViewState = {
   scrollGeneration: number;
   // Optional line number to scroll to in the source view.
   scrollToLineNumber?: number;
-  // Non-null if this source file was opened for a function from native code.
-  // In theory, multiple different libraries can have source files with the same
-  // path but different content.
-  // Null if the source file is not for native code or if the lib is not known,
-  // for example if the source view was opened via the URL (the source URL param
-  // currently discards the libIndex).
-  libIndex: IndexIntoLibs | null;
   // Index into source table. Contains information (filename and uuid) about the
   // source. Null if a function without a file path was double clicked.
   sourceIndex: IndexIntoSourceTable | null;