The Main Advantage Firefox has over IE is that firefox doesn't support Active X & active x scripting. These protocols allow outside software To be run on a machine w/o the software having to be installed on the system.
This means IE is Alot less secure. This is how Nasties like Trogans, spyware/adware get into the system.
I Personally Have noticed I've Had A lot less infestations after installing Mozilla.
It's great, I haven't looked back Since
Jake