I just use the basic Firefox and haven't had a single virus since (knocking on wood). I don't run a real time virus scanner either as it slows everything down. I had virus probs all the time using Explorer.
Some of the Add-Ons REALLY make it good, especially NoScript, Distrust, Chromtabss and Ad Block (Plus, FilterSet.G). No more banner ads and I have control over which sites can run scripts on my system
And sometimes when IE is hanging, FF will work better or vice versa. Or sometimes. I use both
I am not sure why, but Firefox works much quicker than MS Internet Explorer. Been using Firefox for the past 6 months and have not had any problems whatsoever.
Try doing a comparison "test" between the two. I think that you will find that IE 7.0 "hangs" and is slow to boot-up websites, whereas Firefox is way faster!