Firstly, thank you for your great post. Good stuff!

Please, if you allow me a suggestion, it'll be amazing to have, at the beginning of this /c/firefoxcss, a kind of index summarizing CSS/JS sources... just a plain clean index, with titles or subtitles and links to the CSS/JS sources.

I also invite people to add sources and links. For example:

https://firefoxcss-store.github.io/

https://www.userchrome.org/