Jaif, Welcome to sevenforums!
That may be hard to do. You can try going into your router settings and adding the specific web address for the game, but I'm not sure if it will block all of facebook or not. Could at least try it. Otherwise, there are parental controls (Windows family live essentials) that you can set up to block it, but that may be a bit extreme.
Other than that, I just don't know