Give Vertical Tabs a shot. It's faster, albeit no tree handling.
https://addons.mozilla.org/en-US/firefox/addon/vertical-tabs...
I just plugged this in another reply. The latest and greatest can be found at the author's site.
btw... TabCandy is now called Panorama.
Yes, I'm using Tree Style Tabs on FF4 now, it's fantastic once you go over 20 or so tabs.
Re:Firefox 4 is here
by mistermann on Tuesday March 22, 2011 @08:40PM
(#2357317)
Do you have no issues with it on 4? Mine is very buggy, won't open child (or any other) tabs properly, they open non-visible.
1: https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...