Really strange, that anyone has problems with Firefox.
I was there, on day one, when Firefox 1.0 was first released. I started using it then, and still do, without ever having any problem with it.
If I did, I'd do a FULL POWER OFF, reset of my system and then try it again.
I completely shut down my PC every night, so it gets a RESET every 24 hours. That's partially responsible for it running trouble free, day after day.