Silent updates will install all security updates to the browser silently or in background.
This is the Following Google Chrome, Mozilla Firefox also introduced this Auto updates feature in Version 4.
The X King of Browsers ‘Mozilla Firefox’ also maintaining new version updates for improvements in user-interface, security and speed. Google Chrome is the World’s first browser who introduced the concept of silent updates.
the session manager and the tab group add-on which I use extensively.
It seems that I lost all but the current tab group which I'm not very happy about...
These versions can be used to delay getting new features while still maintaining security.
You should use one of these instead of a newer, old, non-ESR release such as Firefox 56.
Also, according to report, Firefox would check for update when you lick the about firefox page even when automatic update is off so that should be avoided.