"Firefly - Core Rules" has been released in PDF format by Margaret Weis Productions -
Firefly-RolePlaying-Game-Corebook (http://rpg.drivethrustuff.com/product/128012/Firefly-RolePlaying-Game-Corebook)
The printed edition can be pre-ordered from Margaret Weis Productions (http://www.margaretweis.com/) or your FLGS.
Having previously published the "Serenity RPG", which is now out of print, Margaret Weis Productions is flyin' back out into the black for more action and adventure with Captain Malcolm Reynolds and his crew.
Keep flyin'! Stay shiny!