I definitely agree that "Firefly" was a scientific/technological mess. The storytelling was so good that I managed to get past it, but I winced a lot. It's too bad, as setting up a plausible 'verse for the same narrative would have been relatively easy. I ended up just retconning a lot in my head. :)
And yes, the two-part recipe for role-playing happiness is:
- The GM and players are in rough agreement about the style of game they want.
- Within the expectations and conventions of that style, the GM keeps things mostly consistent and predictable, so that the players can suspend disbelief enough to experience the world their characters inhabit.
It happens that the closer the game world is to our world, the easier it is (on average) to keep things mostly consistent and predictable. Even a careful, conscientious GM is going to have problems when too much magic (or magical technology) is involved. In Traveller, why doesn't every serious war involve cracking planets with near-c rocks? In a lots-of-magic fantasy setting, why do e.g. armies of foot-soldiers and walled cities exist?* And so forth. Every step you take away from well-known history (or the present day), from well-known science, is an opportunity to accidentally introduce contradictions and paradoxes that send suspended disbelief crashing to the ground. Successful games either involve players who are more interested in "living" in the world as it's presented without too much questioning and envelope-pushing, or a GM who is really, *really* good at thinking on their feet and steering players away from situations that make the problems obvious.