Testing Joomla site changes while site is offline

Sometimes when you need to make drastic changes to your website, you put you site offline, so that your clients get a site offline message and don't see any temporary incorrect configurations.

You as the developer / administrator of the website need to be able to see the live changes. To do this you need to open a new tab / window (and connent to your live site url) in the same browser where you are logged on as administrator doing the backend changes. If you have maintained the browser session correctly the actual current content is generated beneath the site offline message. Other users who hit your site while the site is configured as offline will only see the site offline message, and only you (due to being logged on as administrator) will be able to see the changes.

The essential thing for this to work, is that you need to ensure that you need to have two windows / tabs running under the same browser session.