Using firefox, I was scanning with HouseCall, and I saw that I was infected with some keygen of some sort and another thingy that I didn't get the name of..so I went back to reading some stuff in another tab, after a few minutes firefox SHUT DOWN by itself..I didn't press anything..and based on experience I know some viruses shut down programs that try to clean computers..so would it be possible for a virus to shut down firefox because HouseCall was trying to clean my PC?

btw I have Avast installed