Andy, for some reason I doubt the word 'enterprise' is what you represent. People slam IE all the time and it is not a horrible browser, 5.5, 6.0 or 7.0. If you use Group Policy and other freely available products effectively, your IE implementaion would be solid. No need to switch to a browser that simply isnt ready for enterprise use, because it has no central management. The structure of Firefox is meant to be used on an individual computer and have a profiles transfered if need be. Sure, redirect folders, that works too.
My point is, I am an avid Firefox user, it gets 98% of my time while browsing, the extensions I install are invaluable to me and I can not live without it. To say you deploy an unmanageable product like this across your network kind of scares me. If you haven't heard, Firefox is just as hole-riddled as IE. For an 'enterprises' security, I would rather use Internet Explorer and I think most admins would be too.
As for the topic, I would love support for Firefox, because it is my default browser. I think, in time, OWA Premium will support Firefox.