If you have the option, hosting your own bitlbee instance with bitlbee-facebook plugin [1] could be even better, since you can access it with any irc client you like. The additional benefit of always being logged in (and messages being marked read as soon as the come) is that facebook has no way to monitor your passive usage of their chat service.

[1] https://github.com/bitlbee/bitlbee-facebook