I second Raid's questions. Also, what sort of technology are we looking at? Guns with bullets, guns with lasers, or both? Is there an internet-like network? Cybernetics? Prosthetics?
On that note, I'd also like to throw in my interest. My character began building himself (or possibly herself, as I'll probably pick whatever gender the crew appears to lack) before I'd finished reading all of it.
I'm not very familiar with Firefly, but I know of the concept. I always thought it had interesting potential.