The newer version of Firefox from Mozilla is definitely better than Firefox
3.6 and is definitely worth trying out. Firefox 4 runs on the Gecko 2.0
web platform. Earlier today I downloaded Firefox 4 and put it through
some drills, here is a review of Firefox 4 Beta 1 where you can find the
new features and also the how Firefox 4 fares against other browsers in
web browser benchmarks.

New User Interface:

Firefox 4 sports a completely different interface, some of which are from Opera
and Google Chrome. Firefox 4 has some new buttons and also a unified
menu which is similar to the one Opera 10.6 has. In addition to that the
tabs also default to the top which is similar to Google Chrome.