I nearly fell off my chair when one of our new enterprise customers asked me if we could provide them the app... but with Firefox support because that was all they used.
I worked for this large company, who had just bought another smaller company. Wisely, the smaller companies IT department had moved everyone onto Firefox, but since they had to have access to our new system, which was IE, we had to tell them to move back to painsville.
It broke our hearts, the IT people, and the users. The new system will work on all browsers (except IE6), whenever that will be out.
Out of curiosity, did you look into using something like IETab? You can configure it to render specific sites in IE's Trident engine, and all other sites using the usual Gecko engine.
However, I'm not certain how easy it is to push a Firefox extension + configuration to a large number of Windows machines.
It broke our hearts, the IT people, and the users. The new system will work on all browsers (except IE6), whenever that will be out.