How To : Login To Multiple Facebook Accounts With One Browser
But the browser’s cookies can be tricked by Incognito Window, in this case I am using Google Chrome. Incognito Window is a default feature of Chrome. You can use CookiePie in Firefox.
It’s very easy, just click on button and open a new Incognito Window. Or, press Ctrl+Shift+N. Now, you can login to another Facebook account with Incognito Window.