Relanding with correct bug id - Revert behavior for gonk - Bug 1154591. r=spohl, a=RyanVM

toolkit/mozapps/update/nsUpdateService.js

@@ -660,8 +660,10 @@ function getCanStageUpdates() {
   // For Gonk, the updater will remount the /system partition to move staged
   // files into place.
   if (AppConstants.platform == "gonk") {
-    LOG("getCanStageUpdates - able to stage updates because this is gonk");
-    return true;
+    if (getPref("getBoolPref", PREF_APP_UPDATE_SERVICE_ENABLED, false)) {
+      LOG("getCanStageUpdates - able to stage updates because this is gonk");
+      return true;
+    }
   }
 
   if (!hasUpdateMutex()) {