I run Firefox from a portableapp usb drive. the PortableApp manages Firefox updates. I would like to turn OFF the check for update button that is LOCKED ON BY MOZILLA.

Then the updater mechanism needs to set a policy to disable the internal updates, like many other distributions. If the authors search for enterprise policies documentation, they'll find what they need there.

https://firefox-admin-docs.mozilla.org/ https://firefox-admin-docs.mozilla.org/reference/policies/#device-update-settings

Hello

Take a look at https://www.youtube.com/watch?v=wiWZOm_UX30

I tested

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

Votre navigateur est géré par votre organisation.

DisableAppUpdate https://connect.mozilla.org/t5/discussions/upgrade-notification-spam/m-p/64080/highlight/true#M22529

Other situation, if, the pc target use the Windows registry.

Votre navigateur est géré par votre organisation. Les mises à jour sont désactivées par votre administrateur système