How to login to multiple Facebook accounts:
Every website uses cookies to identify user who are logged in, the browser saves user’s information such as email, username, and password. Likewise with Facebook, this popular social networking also uses cookies, so, by default you can not log in to multiple accounts with one browser Facebook.
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.