A little off topic and not that I think it would happen in Firefly's case but has there ever been a show that got a second chance at a series years after cancellation?
Doctor Who (new one is technically the same show, not a follow-up)
Family Matters (moved to CBS for its last season after ABC cancelled it)
Jericho (brought back for a 7-ep second season)
Scrubs (cancelled by NBC after 7th season, moved to ABC)
Babylon 5 (cancelled by PTEN, immediately offered a fifth season by TNT)
Futurama (season 6 coming this year)
And probably plenty others