it's pretty darn good. The "Session Restore" function is pretty good, and the spellchecker will help many people, but I prefer not to rely on that too much...
I think I'll play around with the new Firefox from time to time, but for now I'm sticking with Opera. Good tabbing system, Session Restore AND Session Saving, and its Mouse Shortcuts totally make the Back and standard interface buttons a thing of the past.
edit - and for chaos' question
Improved tabbed browsing: By default, Firefox will open links in new tabs instead of new windows, and each tab will now have a close tab button. Power users who open more tabs than can fit in a single window will see arrows on the left and right side of the tab strip that let them scroll back and forth between their tabs. The History menu will keep a list of recently closed tabs, and a shortcut lets users quickly re-open an accidentally closed tab.