Hasn't crashed yet, so I'm happy. Auto updates your bookmarks and passwords as it should, and looks like opera/chrome now, though I like the minimalist approach. Like it much better than firefox 3.5 but less than opera just because I have everything hotkeyed in opera. Can't 100/100 the acid 3 even now, but I think it's pretty good, definitely get the beta if you're on 3.5 as it's an improvement.
Compared to chrome I never notice the speed difference (between chrome and firefox) when I go to pages anyways, and if you're computer is slowed down by a browser, then I guess stay chrome, ff 4 still takes more resources.
Edit: oh yeah, slower than opera ofc.
DL Link:
http://www.mozilla.com/en-US/firefox/all-beta.htmlS/S: