@migo, what a coincidence, I'm working on Firefly as we speak
It was the first thing I thought of using this game for, and to be honest, it would work great. Just add quirks/flaws like "Brown Coat Veteran" and "Alliance Fugitive" and add some tech-based skills (other skills, like Animal Herding, could actually just be left in the game as is). Even the profession system could be left as is, just replace "whore" with "companion" and so on (yes, the former is actually a profession in the game).
I'm sorry if I didn't cover the setting or the modular rules in greater detail, I was writing the review from work and didn't have the book handy to go into greater detail. To be honest, I've just read through the modular stuff once and skimmed through most of the history, since I had to get the basic game down for my group to start playing. A&8 definitely encourages adding in new rule modules when you need them and have time to read them though, so this approach is certainly viable.
Without going into every modular rule addition in great detail, I can say they work like mini-games and they each have unique rules that largely leave out dice rolling in favor of a deck of cards and/or poker chips. I ran through most of them on my own, just to get an idea, and each one was a lot of fun and would definitely provide for some great group sessions. A good example of this is with bar-fights, where you get strength, agility and endurance chips to wager, and can use the chips to do different maneuvers against your enemies (headbutts, kidney punches, low blows - about 20 options in total) in an attempt to "win the pot" for the round (aka get the upper hand). It's fast, it's furious, it's evocative and lots of fun. If you start out a campaign of A&8 with a bar-fight, your players will be pleased as punch.
As for the setting, I don't yet know it well enough. To be honest, I'm going to be taking a lot of ideas from it, and making a lot up myself for my group's campaign. If you want a better idea of what it entails, check out the post I made on page 1 of this thread, or hop on over to the A&8 website and check out the interactive map.
Also, there are four pages of wild west slang that I am just noticing now. I find myself finding new stuff in this book that I haven't yet seen quite a bit.