It looks like this problem will need some more diagnosing. Please try Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems. The idea is to disable your extensions and see if the problem goes away. If so, you'll have to re-enable them one by one looking to see which one causes the problem. Let us know if you find either way.

I uninstalled Google Chrome and a couple of other programs last night that I don't use. That seems to have done the trick; Firefox hasn't crashed at all today. I guess this isn't a new problem, based on what I've read.

Thanks for your help. Everything seems to be working fine now.