Yeah, Firefly RPG is a whole different system. It uses "Cortex Plus", where as the Serenity RPG uses an old version of "Cortex Classic" Honestly, the Serenity RPG is a terrible system. There is a newer rule book called Big Damn Heroes that uses a newer "Cortex Classic" version. I run a Serenity RPG that uses the core Cortex Classic system. Cortex Plus is very different. It is far less 'number crunchy' and emphasizes in player storytelling. I bought the pdf for like $15, and haven't looked too into it, but it does look nice. I recommend looking into that system.