Here is the policies documentation.

Manage updates, policies & customization
http://support.mozilla.org/en-US/produc … enterprise

Customizing Firefox Using policies.json
http://support.mozilla.org/en-US/kb/cus … liciesjson

Create a folder called distribution where the firefox.exe is located and place the policies.json file there.

CODE: SELECT ALL

{
"policies": {
"DisableAppUpdate": true
}
}

Customizing Firefox Using Group Policy
http://support.mozilla.org/en-US/kb/cus … cy-windows

Local Group Policy Editor (gpedit.msc) is not available in Home versions of Windows 7, 8 or 10.

How to stop Firefox from showing the update nag screen?
http://superuser.com/questions/1407844

Enterprise Policies
http://klaus-hartnegg.de/gpo/2018-05-26-Firefox-Policies.html

Enterprise Policy Generator
http://addons.mozilla.org/firefox/addon/976971

I never tried the Enterprise Policy Generator addon.

policies.json being removed on browser updates via setup.exe (wontfix)
http://bugzilla.mozilla.org/show_bug.cgi?id=1502188

P.S.

I got the DisableAppUpdate policy working with the policies.json file in Firefox Portable 71.0 32-bit.

* C:\FirefoxPortable\App\Firefox\distribution\policies.json

However, I had to remove the following registry keys before I got it working.

* HKEY_CURRENT_USER\Software\Policies\Mozilla
* HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Mozilla

Here is how to test if the DisableAppUpdate policy is working.

Test DisableAppUpdate policy: viewtopic.php?p=14848020#p14848020

Source: Turn Off Updates • mozillaZine Forums