Fixed: EHH - Filter creating window won't close

chrome/content/composer.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 {Prefs} = require("prefs");
 
 let domainData;
 let nodeData;
@@ skipping 537 matching lines @@
 function togglePreview(preview) {
   if (preview) {
     if (!previewStyle || !previewStyle.parentNode) {
       previewStyle = doc.createElementNS("http://www.w3.org/1999/xhtml", "style");
       previewStyle.setAttribute("type", "text/css");
       doc.documentElement.appendChild(previewStyle);
     }
     previewStyle.textContent = stylesheetData;
   }
   else {
-    if (previewStyle && previewStyle.parentNode)
-      previewStyle.parentNode.removeChild(previewStyle);
+    try
+    {
+      if (previewStyle && previewStyle.parentNode)
+        previewStyle.parentNode.removeChild(previewStyle);
+    }
+    catch (e)
+    {
+      // if the window was closed (reloaded) we end up with dead object reference
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=695480
+      // just ignore this case
+    }
     previewStyle = null;
   }
 }
 
 function changeDomain(node) {
   domainData.selected = node.getAttribute("value");
   updateExpression();
 }
 
 function toggleAttr(node) {
@@ skipping 56 matching lines @@
 
   fillAttributes(item.nodeData);
 }
 
 function addExpression()
 {
   AdblockPlus.addPatterns([document.getElementById("expression").value]);
 
   togglePreview(false);
 }