This is pretty straight forward yet awesome! Get all your friends on a real chat client instead of that annoying and crippled Facebook chat window! All you need to do is install a little package called pidgin-facebook. If you are on a Debian system just download this package and install it using the GUI or the “dpkg -i” command and you are set! If you are on a Red Hat system, use Alien. For anything else just install from source.
You might also want to install the Facebook icons for Pidgin. Extract it to /usr/share/pixmaps/pidgin/protocols