Actually, I liked the song. It fit the show and the genre mash (western+space) that was Firefly.
But then again, there is not a big cross over between CW fans and Sci-fi fans.
That also could of been part of the issue about its viewers, as most sci-fi fans have a knee-jerk reaction to westerns. Many of our fanish kin rejected the show right out, just because it was "western". By the time we could convince them otherwise, it was cancelled.
Then again, Star Trek was pitched as "Wagon Train in Space". Of course, Trek move far, far, against that listing. So I don't know why anyone would have that reaction.