The point is that Firefly had a pretty interesting western inspired soundtrack composed primarily by a dude named Greg Edmonson. Then, in 2011, The Internet's Foremost Comic Book Rapper, Adam WarRock, decided to take that entire soundtrack and release a mixtape of songs that sampled from it. That's right. You don't just get one Firefly related song, you've got basically an entire album of samply-goodness, and it's all free! You can download The Browncoats Mixtape here. The song "Mal" would definitely be the first single released off of it, so check that out below if you want before you grab the whole thing.
The entire concept of Adam WarRock was thrust upon me by the creators of Atomic Robo which I just started reading and think you should too.