Index: lib/inspectorObserver.js
===================================================================
--- a/lib/inspectorObserver.js
+++ b/lib/inspectorObserver.js
@@ -32,8 +32,7 @@
     let stringBundle = Services.strings.createBundle("chrome://elemhidehelper/locale/global.properties?" + Math.random());
     let result = stringBundle.GetStringFromName("inspector.button.tooltiptext");
 
-    delete this.inspectorButtonTooltip;
-    this.__defineGetter__("inspectorButtonTooltip", function() result);
+    Object.defineProperty(this, "inspectorButtonTooltip", {value: result, enumerable: true});
     return this.inspectorButtonTooltip;
   },