Firefly is mythmaking, telling us stories about the world. I compare this with, for example, westerns such as the Shadow books, or the television show Bonanza. They are at best incidentally historical, and often quite ahistorical, serving instead as mythic storytelling cloaked in Western tropes. Firefly is incidentally science fictional, and often quite ascientific, but it is mythic storytelling cloaked in SFnal tropes. This observation of course touches on the Pandora's box of "what is science fiction, anyway?"
For what it's worth, it was the theme song that finally cued me in. Listening to that over and over, I got it.
Naturally this old news to almost everyone reading this, but, hey, give me time. I catch up eventually.