bug(windows): backspace problems in Google Docs using Firefox

Originally reported [here ](https://community.software.sil.org/t/backspace-problems-with-keyman-keyboard-in-a-google-doc-in-firefox/9664/19).
**To reproduce:**
Windows 11 using Firefox.
Use the Tchad QWERTY keyboard (available in the repo) to type in French (associating it to the fr-FR language) .
Open a new Google Doc in Firefox (latest), activate the keyboard, type “Test” and press Backspace, the cursor moves between the “s” and the “t”, but doesn’t delete the “t”.
Press Backspace again, it deletes the “s”.
Notes form post:
If I type “Test” then left arrow and Delete, it deletes the “t” just fine. If I use Backspace multiple times, it deletes some of the letters, but not all. I usually have to clean up remaining letters with the Delete key. If I do the same test in Chrome, it works fine.

This report with Discord may also be [related](https://community.software.sil.org/t/backspace-and-search-bars-acting-weird-on-firefox/10870/21).