Computer Configuration > Administrative Templates > Firefox
Both
HKLM\Software\Policies\Mozilla\Firefox
If this policy is enabled, Firefox will never run SHIELD studies or do Heartbeat surveys. If this policy is disabled or not configured, the user can choose to enable SHIELD studies or Heartbeat surveys. For more information, see https://support.mozilla.org/en-US/kb/shield and https://wiki.mozilla.org/Firefox/Shield/Heartbeat