A little more information about availability from Wikipedia:
"At Mobile World Congress 2012, Mozilla and Telefónica announced that the Spanish telecommunications provider intended to deliver "open Web devices" in 2012 based on HTML5 and these APIs. Mozilla also announced support for the project from Adobe and Qualcomm, and that Deutsche Telekom’s Innovation Labs will join the project. Mozilla demonstrated a "sneak preview" of the software and apps running on Samsung Galaxy S II phones (replacing their usual Android operating system). In August 2012, a Nokia employee demonstrated the OS running on a Raspberry Pi.
Firefox OS is compatible with devices including: Otoro, PandaBoard, Emulator (ARM and x86), Desktop, Nexus S, Nexus S 4G, Samsung Galaxy S II, and Galaxy Nexus."
Be warned, The Nexus S / SGS11 'support' is partial, there are known bugs with both that arent actively being worked on. If you are happy testing out the bleeding edge then these are good to play with. If you want something that guarantees to work (and is high priority when bugs are visible) then I would use the simulator for now until there is some form of more official support for a publically available phone.
That's probably the easiest way.
A little more information about availability from Wikipedia:
"At Mobile World Congress 2012, Mozilla and Telefónica announced that the Spanish telecommunications provider intended to deliver "open Web devices" in 2012 based on HTML5 and these APIs. Mozilla also announced support for the project from Adobe and Qualcomm, and that Deutsche Telekom’s Innovation Labs will join the project. Mozilla demonstrated a "sneak preview" of the software and apps running on Samsung Galaxy S II phones (replacing their usual Android operating system). In August 2012, a Nokia employee demonstrated the OS running on a Raspberry Pi.
Firefox OS is compatible with devices including: Otoro, PandaBoard, Emulator (ARM and x86), Desktop, Nexus S, Nexus S 4G, Samsung Galaxy S II, and Galaxy Nexus."
http://en.wikipedia.org/wiki/Firefox_OS#Demonstrations