Cursor jumps to end of editor when deleting certain text nodes in Firefox #111

Steps to reproduce

• Open Firefox (currently using version 120.0.1)
• Go to https://medv.io/codejar/
• In the code example, move cursor to position indicated by │ and hit backspace:

import {CodeJar} from │'codejar';
                      ^

The space character gets deleted, but the cursor also jumps to the end of the div/editor. This isn't happening in Brave/Chromium, so I suspect it is a Firefox specific issue.

From what I can tell this happens when a whitespace text node gets deleted, but only if it's between 2 non-text elements. This isn't an issue when deleting non-text elements like <span>, or deleting whitespace characters in the middle of multiple whitespace characters in a text node.