I can't use IE9, as I have WinXP, and Google Chrome, which I used to like was a disaster. I reported my problems earlier, and after I cleaned up a virus picked up, somehow, by Chrome, a clean install failed.
As long as 3.6.x is supported, I will keep it. FF5 is a bit faster, under equal conditions, than 3.6.x, but nothing to write home about it. I have switched to Seamonkey, as default, and keep on using it, as long as it is supported.
The concern that all would be lost if Seamonkey crashes is unjustified. I have, yet, to run into a persistent problem with any Mozilla-related browser, and crashes have been very isolated.
My backups are the Firefox and Thunderbird profiles.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:188.8.131.52) Gecko/20110614 Firefox/3.6.18