Folks, if you have not logged into Second Life I urge you to do so. Be warned. It will waste a good deal of your time. Also, there is a Firefly community, the crappy little town named after Hoban Washburne. It's built by residents, populated by residents, and the RP revolves around the residents interactions with one another. I built my own house and rent a plot of land there for my avatar to live.
Second Life is free. You go to secondlife.com and create an account, which involves naming your avatar. You give the avatar a first name and you choose from a list of second names. VERY IMPORTANT: Use a capital letter for the first name or inworld you'll be considered one of those wankers not smart enough to use the shift key. Your will appear as you type it. I'd also recommend you avoid numbers as this isn't an IM service, but a very realistic avatar you'll use to interact with other avatars inworld. Numbers sort of add to the noobiness (new avatar which isn't considered a good thing most of the time as you'll be tore up from the floor up until you get help from someone who has been inworld for a while) and wankiness of your character.
I also recommend you add a credit card to your account because you'll want to buy things. Clothes. OMG. Clothes. You'll want to dress up your Ken or Barbie and I warn you now that this is going to be a huge huge addiction. Hair. I own lots of hair. I love hair. I love hair almost as much as I love clothes.
Beyond the Firefly community, there are other sims to play in from urban ghettos to metropolis-type cities with an array of fantasy characters from human to Neko to vampire and werewolf. The fun part of Second Life is that you get to explore these places and find a sim that works for you, while developing your avatar into a character that is entirely your own.
If you want to come by and see me inworld leave me a comment and I'll give you the info via e-mail. The only thing I ask of you is that you do NOT mention this journal or my fanfiction in open chat once you are inworld. I RP with a couple of RL (real life) friends and they have no clue that I write fanfic or even have this journal and I don't want to deal with them knowing. That said, friend me inworld and I'll help you get rid of the noobiness of your avatar, show you the best places to buy clothes, hair, shoes, and get quality freebies. For about $10 US dollars you can buy about 2589 Lindens--which is the inworld cash used for all transactions. I recommend you buy $20US to get your avatar set up properly. After that, you just buy Lindens when you need them. If you don't plan to have land or a house, don't be surprised if you spend most of the money on clothes and hair for your avatar.