threetonesun parent
You can add any applications to Steam's Big Picture mode and the UI is relatively couch friendly. Yes, you could install Steam on any distro and do this but SteamOS is pretty nice out of the box if you want a TV friendly solution.
Steam Big Picture is very couch friendly, if you're using a game pad and what you're launching supports a game pad. That's why it works for a couch gaming PC. Firefox has pretty bad gamepad support last I checked.
It's been a while since I've had to customize it much but I believe the Steam overlay allows you to map controller inputs to anything, uniquely for every given app you run through it.
That said, at some point I think yes, you just get a bluetooth mouse/keyboard to go with it.
And how well have you been able to get this to work with Firefox?