My parents had a problem with their computer recently: opening an IE window would result in Firefox opening instead. Now, this isn’t really a big problem considering that they use Firefox and don’t care for IE, but they needed it for a particular site, so I had to figure out what the problem was. Fortunately, the Internets is full of answers…
For their computer, deleting the registry key worked, and I had to delete the DLL file (look in the comments). I like to think of it, though, as Microsoft implicitly admitting that yeah, IE really is inferior…