--- a/dom/permission/PermissionSettings.jsm
+++ b/dom/permission/PermissionSettings.jsm
@@ -103,15 +103,20 @@ this.PermissionSettingsModule = {
   receiveMessage: function receiveMessage(aMessage) {
     debug("PermissionSettings::receiveMessage " + aMessage.name);
     let mm = aMessage.target;
     let msg = aMessage.data;
 
     let result;
     switch (aMessage.name) {
       case "PermissionSettings:AddPermission":
+        if (!aMessage.target.assertPermission("permissions")) {
+          Cu.reportError("PermissionSettings message " + msg.name +
+                         " from a content process with no 'permissions' privileges.");
+          return null;
+        }
         this.addPermission(msg);
         break;
     }
   }
 }
 
 PermissionSettingsModule.init();