Issue 3962 - Update developer tools module paths in Element Hiding Helper

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));
+      // Firefox 44+
+      ({gDevTools} = Cu.import("resource://devtools/client/framework/gDevTools.jsm", null));
     }
-    catch(e)
+    catch (e)
     {
-      // No developer tools or unsupported version - ignore.
-      return;
+      try
+      {
+        // Older Firefox versions
+        ({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()
     {
       gDevTools.off("inspector-ready", this.inspectorReady);
     }.bind(this));
   },
 
   get inspectorButtonTooltip()
@@ skipping 42 matching lines @@
 
     //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();