The final version is out and I've been using it for roughly 1.5 minutes now and all I can say is that I'm
very impressed with the speed of the new JavaScript engine. Loading Gmail and the MysteryByte Forums was like a night and day difference from what I was using before; which was version 3.1 I believe.
http://www.mozilla.com/en-US/firefox/firefox.html
*Edit* I just wanted to add the feeling I'm getting right now is the same one I had over 10 years ago when I first switched from Dial-Up to Cable internet. Maybe the difference won't be so dramatic at home as it is here for me at work but wow.