How to prevent automatic update to Firefox 57.0 Quantum?

So at work, my Firefox got automatically updated to 57.0 (Quantum) since I have automatic updates enabled.

Turns out that a lot of add-ons don't work anymore with 57.0, e.g. 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...

Now, at home I use the same add-ons and I'd like to prevent losing my tab groups so I'm looking for a way to disable automatic updates (which are enabled) before I start Firefox so that I get a chance to save/export my tab groups and find a solution that will work with 57.0 before actually updating to 57.0.

How can I do that?

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.

Better off changing user_pref("app.update.mode", 1) to 2

WHY

app.update.mode uses an integer value (default 1) to decide the "behaviour" of updating... if you modify this value you are not:

1. altering the developers code by injecting your own custom code or
2. stopping upgrades altogether

the following is from https://wiki.mozilla.org/Software_Update:Testing

INTEGER - app.update.mode Default: 1 defines the policy by which background downloads are done, and the amount of user prompting that is required: 0 - download all update types (major/minor) without user intervention, regardless of incompatible extensions installed (they should just be disabled after the update restart) 1 - download all update types (major/minor) only if there are no incompatibilities with enabled extensions, prompt with UI otherwise. 2 - download minor updates only, prompt for major updates, regardless of whether or not all enabled extensions are compatible.

an upgrade to quantum is definitely a major upgrade...