Thunderbord and Firefox problems.

For some reason, Avast Free Antivirus has started blocking Thunderbird and Firefox when it's Real Time Shields are on. That's why I could access the web or email on my study PC this morning. For some reason I still can on the lounge PC, and the only difference I can see between the two is that the lounge PC is a 32 bit PC, and teh study is a 64 bit PC. Am trying to find out how I can adjust this and for the moment have both disabled, which I'm not happy with.