custom plugin using add_action works in Firefox only

Custom plugin tracks logged-in users.
Inserts user data into table when user logs in.
Deletes the entry from the table when user logs out.

———
The code:

class activeUsers{
	function userloggedIn(){
          //db insert
	}

	function userLoggedOut(){
	  // db delete
	}
}
add_action('login_head',array('activeUsers','userLoggedIn'));
add_action('wp_logout',array('activeUsers','userLoggedOut'));

———
The Problem:
It works perfectly in Firefox but, the insert (using add_action('login_head',array('activeUsers','userLoggedIn'));) will not occur in any other browser.

———
Debug test:
performed the insert with:
add_action('get_footer',array('activeUsers','userLoggedIn'));
and it works cross-browser.

Running out of hairs to pull. Any insight would be greatly appreciated. Thanks.