Web of Trust
I install the software from mywot.com on all browsers for computers I use. It could reduce the number of dodgy sites people try to visit.
I'm not sure about Avast (mixed reviews - and it failed to detect spyware on a friend's computer) Assuming you stick with Avast, you probably want to disable the Avast toolbars for IE/Firefox/etc and just use MyWOT instead. The AV will still scan downloads, and I don't think Avast has the XSS blocking abilities of paid-for security software so there's little advantage to the browser addon.
Biting the hand that feeds IT
