How to Limit Login Session Cookie to a Single Browser Tab

[dragonsway]

I followed the Virtualmin installation guide to replace Usermin with Roundcube as the default webmail tool.
https://www.virtualmin.com/documentation/web/faq/

Everything seems to work correctly, except the the first user account that log into has its login session validated in only other broweser tabs and windows as (I am using Chromium Web Browser for Ubuntu 20.04).

Here's an example of my problem:

1.) In Browser Window 1, I enter webmail.domain-one.com and it correctly re-directs me to my Vmin virtual server install of RC located at https://email.centralroundcube.com  instead of Usermin. 

2.) I successfully log into webmail.domain-one.com

3.) I open another Tab inside Browser Window 1, and I type in webmail.domain-two.com.... Problem instead of being asked for a username and password at the RC login screen.  I am immediately taken to inbox of webmail.domain-one.com

4.) If I change Browser Window 2 and enter webmail.domain-two.com -again- I am redirected straight to the inbox of webmail.domain-one.com

Whereas if I an Incognito Window and/or different browser and I enter webmail.domain-two.com everything works correctly and I can successfully log into webmail.domain-two.com's email account. 

So re-stating my question:  How do I limit login session cookie validation to a single browser tab?

I read / reviewed all of the RC defaults.inc.php found here, but none of them seem appropriate, unless I am misunderstanding something in my noobish confusion.
https://github.com/roundcube/roundcubemail/blob/master/config/defaults.inc.php

[dragonsway]

If it helps, my current config.inc.php contains the following (perhaps the noob is missing something obvious)

Code Select Expand

$config['db_dsnw'] = 'mysql://XXXX@localhost/XXXX_roundcube';
$config['default_host'] = 'localhost';
$config['smtp_server'] = 'localhost';
$config['smtp_port'] = 25;
$config['smtp_user'] = '';
$config['smtp_pass'] = '';
$config['support_url'] = '';
$config['product_name'] = 'Roundcube Webmail';
$config['des_key'] = 'rcmail-XXXX';
$config['plugins'] = [
    'virtuser_file',
    'archive',
    'zipdownload',
];
$config['skin'] = 'elastic';
$rcmail_config['virtuser_file'] = '/etc/postfix/virtual';
$config['virtuser_file'] = '/etc/postfix/virtual'