If anyone has destroyed anything, that's Mozilla with their decision to drop XUL, not tobwithu. I am frustrated, too, but please, read his notes before deciding to give it a bad rating. Also be aware that there is an issue with black text on dark themes that has been posted in forums.
Re-installing 3.5.x automatically brings your old account settings back (logins, scripts, RSS, etc). - they're not lost, actually (make sure you disable automatic updates on the extension's "More" page).
While looking fwd to see scripting back (or a replacement) and Neo growing mature, I'll use 3.5 for as long as FFox allows it. (If you think it's time to say goodbye, it's maybe time to say goodbye to FFox... although I probably won't. Sad.)