Thank you for your prompt reply Asyn. Your suggestion worked perfectly.
DavidR, the Avast dialogue box would respond to an update command, but then I would get an error message in the lower right of the screen saying that the update attempt failed. I had not thought to go to the Avast website to see if there was a more recent version posted, since my updates up to the point of installing FF5 were current. Since FF5 also disabled other add-ons, I made the assumption that somehow it was not playing nice with Avast AV.
FYI, I am running the Windows Firewall since I am behind two routers. There does not seem to be any conflict such as there was when I ran ZoneAlarm FW. Thank you again, both, for you timely and informed replies.
RM