Due to resist-fingerprinting needed to be disabled to use the website appearance setting in @firefox I was searching for an alternative and found Dark Reader (https://github.com/darkreader/darkreader). I remember using it a few years ago and since then it has gotten pretty darn good. If you want to use websites without your eyeballs melting from the bright light, I’d recommend you to try Dark Reader out.
Also check out Dark Background and Light Text. It lets you customize colors and doesn’t increase load times quite as much as Dark Reader in my experience.
Additionally, if you use a dark system theme and sometimes encounter difficult to read texts (e.g. in form fields), have a look at Text Contrast for Dark Themes.
Yes, can’t browse without it