I'll join the votes for AVG. Quick, doesn''t take up too many resources, doesn't ferk your system like Norton and reliable. I paid for the full story, but the free version is said to be good, though the free update servers can be slow.
AVG also do a combo firewall/AV for not much more, which is a good one-stop-shop (just installed it on a machine I built for someone).
If you want to keep your current AV you could
try saving your Firefox preferences, deleting it FF and reinstalling it, though I wouldn't bet that that will work. Or you could install Opera (arguably the best of the lot) instead of FF.
