Thank you very much again for the clear advice, Michaelrask. I will do so.

Thanks, Pondus. I tried to clear my cache by following
http://support.mozilla.com/en-US/kb/How%20to%20clear%20the%20cache

It went from “Your cache is currently using 357mb of disk space” to seeing nothing displayed.
Nothing seemed to happen, (no progress bar or notification that the cache was cleared),
but i guess it worked because the directory “0” where the infected files were located is no longer there.

Is my cache clear now?

http://i28.photobucket.com/albums/c219/enjay2/Avast/AVASTmozillacache.jpg

unfortunately i wasn’t wise enough to take a snapshot before.