I've seen plenty of speculation, but I think it's been pretty well established that the 'verse is a single solar system. We fled the Solar system on generation ships and arrived elsewhere, another solar system with lots of rocky worlds (not so farfetched, really, for reasons I won't go into here). But where is it?
I've heard some references to 61 Virginis (a.k.a. Gliese 506 or HD 115617). It's a reasonable candidate -- a G6V star 28 light-years from here with a high abundance of heavy elements. Hard to believe there's nothing closer, though.
I saw a couple of graphics supposedly of the Firefly system, but it didn't seem to have all of the worlds found in the Serenity Visual Companion.
Anyone have any info?