I would also use the Alternity system to run a Serenity/Firefly game.
This is for two reasons.
One, I don't like the system used in the book. It feels . . . wonky, for lack of anything else. I also don't like that even when an attribute is rated high, it can still roll as poorly as someone who has a low attribute. Sure, they could roll higher and their average roll is better, but as we all know, sometimes things hang on that one roll.
Two, I prefer Alternity. I am much more familiar with it and I think it would be fun. Further, I use Drama Points, from Eden, instead of LRPs, which I think would help to create that Firefly-esque game. Maybe I missed it but I didn't see anything like that in the game.
Sorry if this was too cryptic.
Have a good one! Take care!
edg