One faction believes the series all takes place within our system and the other believes it is interstellar.

The Solar system faction bases their opinion on the lack of any mentioned star drive and the fact that many of the "planets" are referred to as moons.

I'm no a cult member but I favor the interstellar view. They don't talk about the star drive but neither do they talk about AG and rapid terraforming or the apparent 1 G on all the planets and moons

The silence in space was one of the few things true to science in Firefly and I too have learned long ago not to let noisy rockets and other science flubs spoil the fiction. It was a very entertaining series.