At home I run a custom built HTPC running Ubuntu with XBMC as the main interface. So that the machine boots into XBMC directly, and to avoid any superfluous applications running, I use XBMC directly as the user-session.
Using the Advanced Launcher plugin I was able to launch firefox, but it always launched in what looked like a windowed interface, and only filled about one quarter of my TV. Clicking on the maximise window button had no effect.
The reason that it was doing this was because there was no window manager for Firefox to use.
The solution that I came up with was to install Fluxbox and with the help of the following script.
#!/bin/bash fluxbox& firefox pkill -9 fluxbox
The script starts Fluxbox in the background, then launches Firefox, which uses Fluxbox as its window manager, allowing it to be full screen. Firefox then blocks this script from running until you exit firefox. Fluxbox then ends and you return to XBMC.
Setup the launcher to use this script, and then you can add it to your home screen, and hey presto, easy access to firefox on you TV.