bug 1488593 - disable family safety detection by default r=jcj

As of bug 1346297, we don't collect telemetry for the family safety root
feature. At this point, it makes the most sense to disable the entire feature by
default.

Differential Revision: https://phabricator.services.mozilla.com/D4994

--HG--
extra : moz-landing-system : lando

security/manager/ssl/nsNSSComponent.cpp

@@ -573,8 +573,8 @@ nsNSSComponent::MaybeEnableFamilySafetyCompatibility()
   if (!(IsWin8Point1OrLater() && !IsWin10OrLater())) {
     return;
   }
-  // Detect but don't import by default.
-  uint32_t familySafetyMode = Preferences::GetUint(kFamilySafetyModePref, 1);
+  // Disabled by default.
+  uint32_t familySafetyMode = Preferences::GetUint(kFamilySafetyModePref, 0);
   if (familySafetyMode > 2) {
     familySafetyMode = 0;
   }