This is first time I seen a complaint about FF crashing.
Personally, on my box nothing has even crashed in FC3 or 4.
If you use plug-ins update to 104-4
If the cache is default of 50 MB and you don't clear when closed and haven cleared it for a long time, might be time to do that.
What else are you running with it? It the same program running each time it crashes?
Is SELinux on?