IE is not as modular or customizable as Firefox. IE doesn't follow standards correctly. IE doesn't have transparency in png images. IE can't view scalable vector graphics.
Etcetera etcetera etcetera.
So if you are using Internet Explorer just because "Firefox isn't really better and only an idiot can get a virus", think twice.
Yes, and I know Firefox doesn't have text filters like IE, but thats because IE misused a standard. Firefox will have glowing/dropshadow/etc text eventually, without using flawed CSS standards.