Why does Firefox keep crashing?

I have Firefox & it keeps crashing on me! In fact, it did just a few minutes ago. Whenever it crashes I am always able to get back on with no problems. BTW: I have SUPER Anti-Spyware, AVG & Windows Defender. I do complete scans daily; I also have Spyware Blaster-fully protected. Also, I have Windows Firewall--no exceptations. Any tips would be appreciated! Thanx!