I am a PC user, and Fire fox crashes many times, for no apparent reason.
I have all the requirements- XP, 1GB Ram, and 2GB of free hard disk space, yet Firefox crashes many times. And each time I have to download it again, is becoming a menace.
If you are running Firefox 3.0.1, you are using an extremely outdated version of Firefox that does have many known crashes.
Also, try reading Troubleshoot Firefox crashes (closing or quitting unexpectedly)