User Remains Logged In After Browser Closes

For any others stuck on this: Following the sessions instructions for "files" session driver, I created a directory in application, named ci_sessions. Set permissions to 700.

Then in config.php:
$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_expiration'] = 0; //<-- changed from 7200
$config['sess_save_path'] = 'application/ci_sessions'; //<-- changed from NULL
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = TRUE; //<-- changed from FALSE