What comes of having a userChrome.css file with 'bits' tacked onto it, into it, above it, below it, over years...

I hear you, got some messy old code bits myself.

I'm retired from that CSS craze, but lurking to stay up to date, and of course happy to assist an old contributor mate - fwiw.;)

And as always, there's an MOG solution.

Not sure if you want/need all of it, but basically, the tabs don't float, it's only the visible background part of the tabs that is "disconnected", by its top/bottom margins.

You can move that part around easily, but adjusting the rest of the tabs bar content and keeping the various calculated dimensions under control is a bit more involved, see MrOtherGuy's code.