Why are websites still forcing people to use IE?

DragonTHC writes: "I just visited movielink's website for research. Their site has a nice message saying, "Sorry, but in order to enjoy the Movielink service you must use Internet Explorer 5.0 (or higher) or Mozilla/Firefox with an IE Tab Extension (IE installation required)." While allowing the IETab firefox extension is somewhat progressive, why do companies still force people to use Internet Explorer? Surely the site should work just fine in Firefox? With steady gains in market share by firefox, you would think that webmasters would get the hint. How about any /. users who are webmasters, what are your reasons for forcing IE?"