Thanks for your reply, AnnieD.  : )

I have always known about the cache folders, have gone into them to dig out videos from youtube, etc... lol -- But... I'm surprised I never realized that it could be unsafe to keep stuff in there.

I use FF's 'clear private data' shortcut keys to wipe the cache & other stuff often... But still!

To be honest, this was the first time I was ever alerted about a virus attack on a website!
Guess I felt pretty secure with my AV, and was ignorant about considering the cached files if such a thing occurred.