Bug 336961: fix DOM Inspector leak, patch by Regis Caspar <regis.caspar+bz@gmail.com>, r=jag, sr=neil

extensions/inspector/resources/content/viewers/dom/dom.js

@@ -54,6 +54,7 @@ const kPromptServiceCID    = "@mozilla.org/embedcomp/prompt-service;1";
 //////////////////////////////////////////////////
 
 window.addEventListener("load", DOMViewer_initialize, false);
+window.addEventListener("unload", DOMViewer_destroy, false);
 
 function DOMViewer_initialize()
 {
@@ -61,6 +62,12 @@ function DOMViewer_initialize()
   viewer.initialize(parent.FrameExchange.receiveData(window));
 }
 
+function DOMViewer_destroy()
+{
+  PrefUtils.removeObserver("inspector", PrefChangeObserver);
+  viewer = null;
+}
+
 ////////////////////////////////////////////////////////////////////////////
 //// class DOMViewer