With IE, they can do what they want. If you type in a wrong URL in IE, Microsoft decides what should happen next. Obviously they will redirect you to one of their sites (msn search). With FireFox, they don't have those options.
Besides, if they can make their IE a default on each computer, then they can decide on functionality and standards. Ergo, people have to make their sites like Microsoft wants it. And we don't want that don't we?
