How to block Facebook Beacon
Fortunately Nate Weiner figured out an extraordinarily simple solution (for Firefox users). Just install the BlockSite Firefox add-on and block Facebook Beacon.
Weiner was playing an online game the other day when he noticed a pop up window telling him that the web site was going to share his information with his Facebook profile. He had an option to say "no thanks," but like many people, Weiner figured he'd rather not get the message in the first place. So he found the offending requests were sent to "http://www.facebook.com/beacon/beacon.js.php." So you could either add that URL to your BlockSite blacklist, or better yet, add "http://www.facebook.com/beacon/*" to block any requests to the entire Beacon folder.
And now you have your privacy back. For now.