You don’t have to open it.
There is way to install it by booting from a special usb-stick. ITs fully automated, actually. 😉
Anyway, firefly can stream m4v,mp4 video files too, so if the apple TV can access iTunes shared videos, then it should pickup firefly too. (Not sure about that either)
I think the appleTV is a really nice device, and personally think of getting one. So please keep me (and the rest of the gang here) informed about any progress or caveats 🙂