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

lib/inspectorObserver.js

 /*
  * This Source Code is subject to the terms of the Mozilla Public License
  * version 2.0 (the "License"). You can obtain a copy of the License at
  * http://mozilla.org/MPL/2.0/.
  */
 
 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);
     onShutdown.add(function()
     {
@@ skipping 22 matching lines @@
     button = panelWindow.document.createElement("toolbarbutton");
     button.setAttribute("id", "ehh-inspector-toolbarbutton");
     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();