Have you installed Chrome? You check a box and click a button in Firefox, and it launches another program to install Chrome, which asks for no confirmation or installation location.
I'm not used to my browser launching applications without downloading it and it asking me if it should be run first.
Rule #1: Users are stupid.
They don't know WTF they're doing and when software ends up on the computer that offers to be their default browser and all of a sudden, their menus are gone from the top of "the Internet", they ask for help, and someone has to show them what they did so they don't do it again or configure the computer/domain so that it can't happen again.