Issue 2737 - Fix invalid left-hand side error in Firefox 41

lib/inspectorObserver.js

Index: lib/inspectorObserver.js
===================================================================
--- a/lib/inspectorObserver.js
+++ b/lib/inspectorObserver.js
@@ -6,17 +6,17 @@
 
 let InspectorObserver =
 {
   init: function()
   {
     let gDevTools;
     try
     {
-      ({gDevTools}) = Cu.import("resource:///modules/devtools/gDevTools.jsm", null);
+      ({gDevTools} = Cu.import("resource:///modules/devtools/gDevTools.jsm", null));
     }
     catch(e)
     {
       // No developer tools or unsupported version - ignore.
       return;
     }
 
     gDevTools.on("inspector-ready", this.inspectorReady);
@@ -49,18 +49,18 @@ let InspectorObserver =
     button.setAttribute("class", "devtools-toolbarbutton");
     button.setAttribute("tooltiptext", tooltiptext);
     button.setAttribute("tabindex", "0");
     button.addEventListener("command", function()
     {
       panelWindow.openDialog("chrome://elemhidehelper/content/composer.xul", "_blank",
                              "chrome,centerscreen,resizable,dialog=no", panel.selection.node);
     }, false);
-    
+
     //Override button style for light DevTools theme
     let style = panelWindow.document.createProcessingInstruction("xml-stylesheet", 'href="chrome://elemhidehelper/skin/devToolsOverlay.css" type="text/css"');
     panelWindow.document.insertBefore(style, panelWindow.document.firstChild);
-    
+
     inspectBtn.parentNode.insertBefore(button, inspectBtn);
   }
 };
 
 InspectorObserver.init();