How to prevent automatic update to Firefox 57.0 Quantum?

The solution to disable automatic updates without running Firefox is as follows (OS is Windows):

• Edit the file prefs.js, located in %APPDATA%\Mozilla\Firefox\Profiles\xyz.default\ which usually translates to C:\Users\username\AppData\Roaming\Mozilla\Firefox\Profiles\xyz.default\ (Note: username and xyz will vary)
• Make sure the line user_pref("app.update.enabled", false); is present in the file; if it isn't, add it or modify it. Ignore the warning that this file should not be edited
• Save and close the file
• Start and use Firefox without having to worry about automatic updates
• Optional: Note the button "Check for updates" in the "About Firefox" dialog box. Of course, DO NOT click it until you are prepared and ready to receive the update

An alternative solution to blocking all updates, is to move to a fork of Firefox which will keep the XUL add-on format, now called "Legacy" by Firefox, while still installing security updates.

Two Firefox forks that keep the legacy add-ons are :

• Waterfox (the one recommended by Mozilla)
• Pale Moon

I have tried Pale Moon, and it very nicely imported all my add-ons and profile data. Screen layout was lost and so some small customizations were still required, but in general this is now an exact duplicate of my Firefox version 56, except that it still does security updates.