We wanted to install Firefox on a batch of new PCs yet still have our users think they were using Internet Explorer. It was a real pain in getting it to work, and we eventually gave up but started adding our findings to this website. From there corporate sponsors became interested.
The difference between an IE theme and Firexplorer is saving time and energy. The IE theme typicaly doesn't install for all users, and the Firesomething extension doesn't either. Finally, the Icon packs for Mozilla aren't always straight forward to install properly, and the three of these products aren't soeasy to find.