When you set a Boolean session variable when a user logs in in PHP like:
$_SESSION['logged_in'] = true;
Since this session variable is a Boolean and not a number, and Session variables are stored onto the server not the user Computer, I expect that any browser(user) visiting that site where somebody(another browser) has already logged in, should automatically be logged in since the session variable has a Boolean value of true and not a unique number for different users and has already being set on the server.
How does the server identifies that a particular browser has not visited the site even though a Boolean Session has been set.