No. It's because IE does the best job at rendering what comes out of Microsoft IDEs.
I don't really like that statement - it was late when I wrote it and that is not really what I meant. It should be MS's rendering of the standards is now the industry standard.
Join us in reality, Comrade. The vast majority of content is target toward IE - even content NOT created with MS tools (my company has many products written in Java and other non-MS technologies running on Unix platforms but we only support IE). No business can create web content without making sure it works perfectly in IE. Most business software only supports IE. The only way FireFox can make a major impact is if it can work "just like IE" and like I said: how can a free browser that works just like IE knock Microsoft off its pedestal?