Firefox still is the best browser for powerusers, hands down.
Why yes, I am one for inflammatory statements.
Check out some of my picks
- https://addons.mozilla.org/firefox/collections/cjdmax/user-interface for some very nice UI improvements
- https://addons.mozilla.org/firefox/collections/cjdmax/d for must-have webdevelopment addons
- https://addons.mozilla.org/firefox/collections/cjdmax/privacy for some privacy and security enhancements
All of the above addons are compatible with Firefox 5 (the 'beta' release track), or at least should be; check the developers websites for more up-to-date versions if not.
Addons.mozilla.org (or A.M.O in the lingo) remains an underappreciated website. It has lots of fun and useful functionality, including the 'collections' thing I just used.