Here's my commented Firefox userChrome.css - in case someone might find it useful, you should ignore the browser background thing at the bottom probably - it needs some userContent.css rules to go along with it.
I've been remaking it all since FF 57, so it's pretty limited right now. Pic related is what my FF looks like.
https://hastebin.com/oruvoseman.css>>7063295Thanks, I'll take a look at that - shame Mozilla won't just implement CSS to handle this though :(.