Digital Grabber compared Firefox versus Internet Explorer in a Corporate Network:

The advantages of the IE are mainly founded in its tight integration with Windows. Firefox has to run on other operating systems, too. Hence, all features should work on all systems not only on Windows boxes. That's why I'm not expecting too many improvements in this field in the near future. Although projects like Firefox ADM show that better integration is doable and that some Open Source programmers recognized this problem.

All in all, I'm still a Firefox fan, but wouldn't recommend it for corporate use in larger networks. There are exceptions of course: If all your desktops use Linux or Mac OS. But if you have Windows desktops, the only reason I could think of, is that you really need a certain feature of Firefox which you is not available in IE.