one-tab or supatabs extensions
SuperTabs is Chrom{e|ium} only which doesn't help as I'm moving to FF. OneTab looks partly useful, but often where I came from is important as well as the current tab location, if I've travelled through links “normally” rather than opening in a new tab every time, and I wouldn't expect it to keep that history.
Really, I need to get away from using tabs for long-term state rather than finding a better way to use tabs for that. It would make switching UA easier when I want to, and switching machine too for that matter.
Also, I've been burned by tab and/or session management extensions going stalky (TheGreatSuspender & friends), or stagnating and failing after a time.
I want to move as much state beyond active interactive use away from the browser. I've never kept passwords there or gone in for built-in sync options, but feel the need to take this further. The older I get, the more I see tight integration as a lock-in rather than a benefit.
I'd not encountered anything broken in Chrome that was fixed by FF though.
I'll still be primarily Chrome in DayJob though, as most of our clients' users are (with some on Edge, a few using FF, and a couple of idiots still not off IE though we don't officially support that) so that makes sense even though I very rarely touch anything front-end these days.