Why Firefox dumped corporate users

From a BBC story on UK government being ripped off on IT:

I'm a civil servant and have to use these IT systems. For all the money that is spent on them I'm using a machine that's 7 years old, has minimal memory and hard-drive capacity, is running Internet Explorer 6, has snail's pace connectivity speed and find it really difficult to do my job. And as you all may know, everything is done on computers these days.

Corporate use = browser fossilisation.