Try using Zen, it’s basically Firefox with vertical tab groups.

Absolutely, that’s basically the same thing

I once switched from Debian i386 to amd64 in-place. That was MUCH harder than you would expect, I guess somewhere between medium and hard in your list. That server is still running that install btw, so in the end it all worked out.

That is a very useful article, thanks for linking it!

Good on you for getting it fixed. One of the reasons Linux is a great OS in my opinion is that everything is in the file system and not in some arcane hidden thing. So every problem is solvable without a reinstall if you’re motivated enough to figure it out.