I added the Mozilla/Firefox repositories from https://launchpad.net/~ubuntu-mozilla-daily/+archive/ppa
... to my Xubuntu (Lucid) /sources.list
While the official new version of Firefox is 3.5.6
Firefox 3.6 is Beta 4
And, I am testing the still in pre-Alpha of Firefox 3.7
I like FireFox 3.7 ... it is even faster than Chrome browser and with more add-ons, themes and extensions than before.
And still seems to be stable, I've had no problems or crashes with 3.7