Bug 344872: Mail window is leaking folderObserver on shutdownm, patch by Adam Guthrie <ispiked@gmail.com>, r=bienvenu

mail/base/content/msgMail3PaneWindow.js

@@ -869,6 +869,8 @@ function OnUnloadMessenger()
   // FIX ME - later we will be able to use onload from the overlay
   OnUnloadMsgHeaderPane();
 
+  OnUnloadFolderPane();
+
   OnMailWindowUnload();
 }
 
@@ -1153,6 +1155,12 @@ function OnLoadFolderPane()
   folderTree.addEventListener("mousedown",TreeOnMouseDown,true);
 }
 
+function OnUnloadFolderPane()
+{
+  var folderTreeBuilder = GetFolderTree().builder.QueryInterface(Components.interfaces.nsIXULTreeBuilder);
+  folderTreeBuilder.removeObserver(folderObserver);
+}
+
 // builds prior to 12-08-2001 did not have the labels column
 // in the thread pane.  so if a user ran an old build, and then
 // upgraded, they get the new column, and this causes problems.