Also, if you already have AdBlock Plus for firefox installed, try this: http://lifehacker.com/5542041/block-sites-from-using-your-facebook-login-with-adblock-pl

Also, if you already have AdBlock Plus for firefox installed, try this: http://lifehacker.com/5542041/block-sites-from-using-your-facebook-login-with-adblock-plus http://lifehacker.com/5542041/block-sites-from-using-your-fa... Prevents non-facebook domains from knowing when you are logged into facebook.