Firefly Canceled and Buffy Greenlit at Multiverse
clipped from kotaku.com Multiverse were working on a Firefly MMO. We say "were", because as of today, that project's been "delayed" the company have announced they're working on a Buffy title
This is a bad move on Fox's part in a long list of bad moves. Buffy may or may not be more popular than Firefly, but it will not be easy to turn it into a game that relates at all to the mythos of the series.
Even if the game takes place after the final season, you still have the limit that only women can be slayers, and magic use has a price so high it would turn more characters into NPC villains. I am not sure what is happening with this decision or why.