When did it start? Try re-installing Firefox and see if it persist. Whenever Firefox crashes on startup, I usually have YouTube open when this happens, reinstalling fixes it, without affecting my addons or settings.
If you have NoScript, hit "temp allow all scripts", or w/e it is and see if the problem persist.
If you have NoScript, hit "temp allow all scripts", or w/e it is and see if the problem persist.