Found via librarian.net, instructions on how to block Facebook Beacon on the browser level (in Firefox). Beacon is one of the things powering the new Facebook social ads. Go read more about how it works, and why you might want to do more than just adjust the privacy settings in Facebook. (Which you can’t even do until one of the external websites using Facebook Beacon tries to send stuff to your profile, thus rendering the privacy settings nearly useless, in my opinion.)