[quote=@Mahz]
[@Grimhildr] Does that mean you can replicate the issue in a fresh Firefox profile window / incognito window (whichever way you can create a window without add-ons)?

If not, then another possibility is that, since Firefox add-ons auto-update, an older add-on could be causing problems now that it wasn't in the past. 
[/quote]

well i just actually disabled every addon i have, and i can't replicate the issue, so i'm gonna have to slowly enable and disable each addon (one at a time) and see which one(s?) causes it.

edit; so, it actually turns out it's an addon called "grammarly" causing it. that sucks.