Even though I have actively touted Firefox several times on this forum, I have to say that I believe that currently IE is better for corporate businesses than Firefox.
IE has a huge support structure in place, generally office applications are designed with IE in mind, many businesses use ActiveX. In the business world where IE is the browser by default, there is no reason to change it. For a company to try and support Firefox would be quite an upheaval, people would have to be trained to support it, and people would have to be trained to use it.
Surprisingly few people in business are computer "techies" and so Firefox would come as something of a shock to the system for them to use.
While I think support will grow for Firefox, I think it will be a long while before, and even if Microsoft are toppled as the browser of choice for business.
I know you are trying to prove otherwise, but always remember to give a fair critique of both sides of the arguement