As Kotaku argues, the hoax was perpetuated by The Yes Men, a strongly anticonsumerist group that apparently thought the best platform for this particular parody was a relatively obscure science fiction show. At this point it's not clear exactly what statement the group was attempting to make, although some sort of spoof on Kickstarter seems the most likely target. Either way, hopes for a Firefly MMO remain unrealized -- and at this point if such a game ever does get approved, we won't believe it's real until it's on the shelf.
[Update: As fans of the franchise point out, FUO representatives have updated their Facebook page with what they allege is a screenshot of the game and an explanation for The Yes Men's involvement. What do you think? Is it a hoax or is it legit?]