How to use Adblock Plus to block other Web sites' access to Facebook
You can use Firefox's Adblock Plus add-on (https://addons.mozilla.org/en-US/firefox/addon/1865) to prevent any other Web site from talking to Facebook when you visit that site. Just install Adblock Plus and then add the following filters:
||facebook.com/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
||facebook.net/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
||fbcdn.com/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
||fbcdn.net/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
The above filters tell Firefox never to allow any site other than Facebook's four sites (facebook.com, facebook.net, fbcdn.com, and fbcdn.net) to access Facebook. Thus, Facebook continues to work perfectly, but other sites don't get to talk to Facebook at all.