Issue 4533 - Don't rely on the default namespace to be XUL for DevTools

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()
   {
@@ skipping 43 matching lines @@
 
     let insertBefore = inspectorToolbar.firstChild;
     let inspectorAddButton = panelWindow.document.getElementById("inspector-element-add-button");
     if (inspectorAddButton && inspectorAddButton.parentNode == inspectorToolbar)
     {
       // Firefox 48+
       insertBefore = inspectorAddButton.nextSibling;
     }
 
     let tooltiptext = InspectorObserver.inspectorButtonTooltip;
-    let button = panelWindow.document.createElement("toolbarbutton");
+    let button = panelWindow.document.createElementNS(
+      "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul",

[saroyanm, 2016/10/17 12:02:09]

LGTM

+      "toolbarbutton"
+    );
     button.setAttribute("id", "ehh-inspector-toolbarbutton");
     button.setAttribute("class", "devtools-toolbarbutton");
     button.setAttribute("tooltiptext", tooltiptext);
     button.setAttribute("tabindex", "0");
     button.addEventListener("command", () =>
     {
       let node = panel.selection.nodeFront;
       let target = panel.target;
       if (node && target.form.elemhidehelper)
       {
@@ skipping 14 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);
 
     inspectorToolbar.insertBefore(button, insertBefore);
   }
 };
 
 InspectorObserver.init();