AppAutoUpdate not available in local group policy editor
I abandoned my effort to control policies using a policies.json file, since the posted instructions do not work and the moderator who was helping me didn't have any additional suggestions. So I'm now trying to do this via the local group policy editor in Windows 10 Pro with Firefox ESR 78.6.1.
I obtained the admx/adml files for that version of Firefox and placed them in the appropriate location in Windows\Policy Definitions.
Now I get the full list of polices in Firefox about:policies#documentation. There is also a Mozilla>Firefox node in the group policy editor with many options. However, AppAutoUpdate is not among them, even though it appears in the documentation. The only thing relevant at all in the GPO editor is Mozilla>Firefox>Preferences>app.update.auto, which both the GPO and about:policies says is deprecated and not supported.
So what is the actual truth? Is there, or is there not really an AppAutoUpdate policy that we can actually use to stop the endless pestering about updates in an ESR version? If there really is one, what are the actual steps to find it and make it work?