1. Remove all shortcuts to Internet explorer from the start menu, mydocuments, desktop, and search menus.

2. Install latest version of firefox, use IE themes.

3. Make a shortcut to start firefox, but change the icon to internet explorer, the retarded blue 'e' symbol.

4. Make sure you get all the bookmarks copied over.

5. Make sure any buttons, keys or special behavior moved to equal features on firefox.

6. Also put some firefox shortcut icons around the start menu and desktop.

They won't even notice anything is different, and if they do, tell them they had to radically update it so that it would be more secure and faster.

If they were tech savvy enough to notice what you were doing, they would have the skill to change it back, and most likely would be already using firefox.