Seriously. My brother, cousin, and mom (as good examples of virus-prone computer users) use Firefox, and very rarely (if ever) have any issues/trojans/breaches. My Dad uses Internet Explorer, and gets a virus every other week. I don't know why he won't switch. Refuses to.
I wouldn't touch IE with a ten foot pole (unless I'm fixing someone's computer... in which case I'll just install Firefox over it. >_>)