This is a thing that really agravate me, the proliferation of “i like it” buttons and comment windows that ask me to log on facebook, or simply websites that use your facebook session to log you in.
So here is a cure, for those who use any ad blocker compatible with AdblockPlus rules (AdThwart on chrome) simply add the following custom rules:
||*.facebook.*^$domain=~facebook.com|~127.0.0.1 ||facebook.com/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net ||facebook.net/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbc ||fbcdn.com/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.netdn.net ||fbcdn.net/*$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
Those rules will tell your navigator to block anything coming from facebook’s hosts, unless you are actually visiting facebook.