Logout link or button

Hi all, i need help for customizing my site, what i need is a logout link or button in my main menu, when user klik on it its will loging out from both site (main site and facebook). i canot use a joomla user logout link because its does not logout from facebook user login.

so i need just like button logout like in JFBlogin module, i want put it in main menu. can some one show me how to make it ?

(sorry for my bad english)