For some time I have been plauged by a slow (3-4 minute) startup window for Firefox.
I have tried numerous fixes suggested online; switching of automatic updates for extensions, clearing down cache and history, even a re-install; but nothing worked. As the problem got progressively worse, my workaround became to start Firefox and then, whilst I waited for it to grind into life, to start Google Chrome and use that to check Facebook, Twitter, etc. Not exactly a fix, but at least I didn’t have to sit and wait as my …

About half way down this thread there is a solution to the slow start-up that many users of Firefox 3 are experiencing.
Works for me, bring FF3 back the top of my browser tree.