This was an issue years ago, and it was fixed. I don’t recall what was the underlying problem or what were the bypasses to make it work till it was fixed.
Unfortunately, with latest FF updates, this regression raised his ugly head, although I was sure it was dead for so many years.
Can anyone remember what is the temporary fix? Currently had to switch to light theme, which looks odd and out of place with all dark themed system (for the winter).
I havent needed to use this any time recently either I dont think, but here are a handful of options
https://wiki.archlinux.org/title/Firefox/Tweaks#Unreadable_input_fields_with_dark_GTK_themes
Are you talking about the AUTO theme? or did you apply a Firefox theme?
AUTO hasn’t given me issues for a very long time… be sure to test this with a new profile, or create a fresh user on your system. (I’m on Plasma testing too).
I’m confident this is an issue with your Home folder.