Can you enter about:policies in the URL bar and paste here your active policies? Thanks.

Thanks! DisableAppUpdate is active. Can you tell me how to deactivate?

See:

• https://github.com/mozilla/policy-templates/blob/master/README.md

You can inspect the Mozilla and Firefox keys with the Windows Registry Editor in HKEY_LOCAL_MACHINE and in HKEY_CURRENT_USER with the Windows Registry Editor to see whether GPO policy rules are active.

• HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Mozilla\Firefox\
• HKEY_CURRENT_USER\SOFTWARE\Policies\Mozilla\Firefox\

The mere presence of the "Mozilla\Firefox\" key is sufficient to make Firefox display this notification, so if you have the Firefox key then remove it and only leave the Mozilla key or remove this key as well if it is empty.

• HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Mozilla\Firefox\ =>
  HKEY_LOCAL_MACHINE\SOFTWARE\Policies\