Unfortunately, money is the main driver here. Sci-fi shows cost ALOT of money to make/produce. If fans show support for a cartoon, it is no sweat for a station to pick it back up, since it is so cheap to make in comparison to live-action. Same thing for a sticom. Even if fan support is phenomenal for a high-budget show, if the ratings aren't there to match the finances, the fans are fighting a losing battle. I am more interested in bringing the show back more than another movie (although another movie would be totally schweet.)
It was truly unfortunate that Firefly had to be on FOX. If it would have been on Sci-Fi, it would still be on. I still cannot understand first, why Joss Whedon didn't try to get the show onto Sci-Fi, and secondly, why didn't Sci-Fi pick the show up???