Well, I have old Windows-XP with (disabled) IE-6, but always use Firefox. If anyone is (for some odd reason) using some version of IE, would they somehow neglect to also have Firefox? Such neglect would be just plain stupid. If they can't get through with IE, they could simply try with Firefox.

If they are too stupid to use this simple solution, maybe you do not wish them to be using your product, since their stupidity will cause them to make endless service requests, and issue many complaints when they cannot get things to work.