Computer Configuration > Administrative Templates > Firefox
Both
HKLM\Software\Policies\Mozilla\Firefox
If this policy is enabled, the Firefox Terms of Use (https://www.mozilla.org/about/legal/terms/firefox/) and Privacy Notice (https://www.mozilla.org/privacy/firefox/) do not display upon startup. You represent that you accept and have the authority to accept the Terms of Use on behalf of all individuals to whom you provide access to this browser. If this policy is disabled or not configured, the Firefox Terms of Use and Privacy Notice do display upon startup.