> I blow some people's minds when I tell them about tab groups (ctrl+shift+e) in Firefox.

What do they think that icon to the right of the tabs is? Just some bit of abstract art? :)

I have a heavily customized userChrome.css - none of Firefox's Chrome UI is exposed to me. The only UI I see are the few context menu options I left and tab groups (if you can consider that FF UI)

It's a lot like Pressing F11 without the issues that arise when using Full Screen browsing.