This is not for general usage, but an „admin-Jumphost“-computer/vm which needs to get flash enabled from time to time and is never used for public internet browsing…
There it might be an un-dogmatic solution to install the last Firefox 78.15 ESR Release.
Find it here: https://ftp.mozilla.org/pub/firefox/releases/78.15.0esr/win64/de/
Disable Auto-Update
That’s easy
- Firefox Settings => Update Settings => „Disable Automatic Updates“
Disable Update-Notification
That’s harder – Firefox guys (think to) know better what’s good for their users and they don’t even provide an „about:config“-switch: fail!
Add the following registry Key:
HKEY_LOCAL_MACHINE\Software\Policies\Mozilla\Firefox
Add the following 32-Bit DWORD
DisableAppUpdate
with value set to
1
and restart Firefox.