ever since i've updated to ff3.01 it's been pretty fast and no crashes. the crash that you're experiencing could probably be from an unclean install. download the new ff3.1 and back-up your bookmarks. uninstall ff2 or ff3 that you have now. delete any old file directories of ff in your profile. install the new ff3.1 and it's as stable as an aircraft carrier out in the big blue ocean.
if you're using xp updating to sp3 might help or maybe the windows registry is quite messy and needs a clean installation.