If you want the Firefox browser to not only notify you before installing any new updates, but also disable automatic download and installation of the updates then, select ‘Ask me what I want to do‘ radio button. Firefox will notify you about new updates for:
3> Search Engines
and give you an option to download and install them. You may accept or deny according to your preference.
To turn off the notification, select the option: “Automatically Download and Install the Update” option.
Related reading: Turn off automatic Firefox updating / download.