I find Firefox 3 slower that Firefox 2. I do not see that the Operating System openSUSE-11.1 Linux has anything to do with it, but rather it is the application itself (unless it is ipv6 as pointed out by caf4926 and a59). Here are some tweaks to firefox 3 you could consider (basically the 3 note below are just the same thing over and over):
I applied the above, found a speed improvement, although I still find firefox2 faster than firefox3. However IMHO firefox3's improved features make the slight speed slow down (with firefox3) more than worth the upgrade from firefox2.