Now I don’t know why you would want to do it, but it is possible.
We all know someone that is just a little too comfortable with that blue “e” but maybe there is something we can do about it. People love to use themes for Firefox and you will be able to use them to make it look like an entirely different browser. You can tell from the screenshots just how realistic it looks in both the Luna theme and the Classic Windows theme. I know plenty of people that would not be able to tell a difference.
Maybe this is the way you trick those family members that are scared of Firefox into using the better browser?