The primary reasons someone would use a third party product like Firefox that is so similar in function to IE on a computer running Windows are:
It's not a Microsoft product.
It's not an American product.
Whatever the perceived advantages, they are far outweighed by support issues, both for the user and infrastructure personnel. There is a case to be made for UNIX vs Windows in many applications, with a huge impact on infrastructure support but life is too short for most people to dick around with Firefox. Anyone who has that kind of time needs more to do.
It's not a Microsoft product.
It's not an American product.
Whatever the perceived advantages, they are far outweighed by support issues, both for the user and infrastructure personnel. There is a case to be made for UNIX vs Windows in many applications, with a huge impact on infrastructure support but life is too short for most people to dick around with Firefox. Anyone who has that kind of time needs more to do.