once I found out there was a Firefly game, publisher Margaret Weis pulled the product? Well, here's someone else who might have thought the same thing, and he cooked up his own version of a Firefly RPG. And posted it for free.
I'm talking about WrathofZombie, who also likes burgers and zombies. Not necessarily in that order or mix, I figure. He wrote a game on zombies too. But concentrating on the Firefly game - it looks fair, with many pages and some bootlegged photos.
Rules are based on Green Ronin's AGE, or more particularly Dragon Age, and Mike Evans (WoZ) makes no secret of it. Copyrights are respected, but this game is produced without permission. The game is free, fan fiction game, and I'd say some good free advertising for a canceled great TV series, a canceled Firefly game, and a nice publisher.
Have a look and see if it helps you running the 'Verse.