Bug 726347 - [Page Thumbnails] add preference to disable capturing thumbnails in the background; r=dao

browser/base/content/browser-thumbnails.js

@@ -26,6 +26,11 @@ let gBrowserThumbnails = {
   _tabEvents: ["TabClose", "TabSelect"],
 
   init: function Thumbnails_init() {
+    try {
+      if (Services.prefs.getBoolPref("browser.pagethumbnails.capturing_disabled"))
+        return;
+    } catch (e) {}
+
     gBrowser.addTabsProgressListener(this);
 
     this._tabEvents.forEach(function (aEvent) {