Firefox 4 Beta
Revamped interface will be familar to Opera users
Menu bar replaced by a "button" which saves on scree real estate
Panorama for tabs allows for intelligent tab grouping
Organize those bookmarks!
A simple but handy feature that shows you where links for right in the address bar - very useful!
Not much change in the Options dialog ...
Add-ons page gets a serious revamp ... very nice and easy to use