I only use Firefox. So it's probably not just that in itself. It sounds like you're using something that adds enables a dark mode preference to Firefox - and c

I only use Firefox. So it's probably not just that in itself. It sounds like you're using something that adds enables a dark mode preference to Firefox - and currently some of the Firefox addons and Chrome disagree about some of the finer details of how that should process. Try it without asking for dark mode.