I don't think Google TV uses Android as the operating system. Which is what is required to run Firefox on mobile devices.

I was curious about this too. I have the Logitech Revue, and I'm annoyed by Chrome, and the advertisements. I was looking up some stuff on Google about these devices, and there is an Update that puts Android Market on these sets, and allows you to download certain apps. They just released an update (For my device, atleast, not sure about the Sony TVs) which update the Android OS to 3.0.1. which is designed for devices with larger screens, or tablets. They havent done much work on the Google TVs, but apparently they're starting to. From what I've read....

Not yet. Google TV has recently been updated to Android 3 (on both the Logitech Revue and Sony TVs), which can support android apps, but Firefox hasn't been added to the android market yet on those devices.

I'd be surprised if Mozilla or the community isn't working on converting the app to run on Google TV, given that it's available as an app download for other Android devices already.