privacy.userContext.extension is extra forbidden!

conf/firefox-forbidden-policies.js

@@ -63,6 +63,10 @@ lockPref("privacy.resistFingerprinting.letterboxing", true);
 //pref("privacy.resistFingerprinting.pbmode", false);
 clearPref("privacy.resistFingerprinting.pbmode");
 
+// Which extension requires container tabs? My policy and this file. This
+// particular option is so forbidden, it cannot be set either in the policy
+// or autoconfig.js
+lockPref("privacy.userContext.extension", "");
 // Enable containers without extensions (although those are forced by the
 // policy. TODO: Remove these as they are in the policy, but disallowed by
 // current ESR

etc/firefox/policies/policies.json

@@ -668,6 +668,12 @@
         "Type": "boolean",
         "Value": true
       },
+      "privacy.userContext.extension": {
+        "Comment": "Displays in settings which extension requires container tabs. None. it's this policy. Preference not allowed for stability reasons.",
+        "Status": "locked",
+        "Type": "string",
+        "Value": ""
+      },
       "privacy.userContext.ui.enabled": {
         "Comment": "Tab containers UI without extensions",
         "Status": "locked",