Bug 420770 Can't open saved message (regression from bug 412822) r=Mnyromyr

mailnews/base/resources/content/mailWindowOverlay.js

@@ -1326,7 +1326,7 @@ function MsgOpenFromFile()
      return;
    }
 
-  var uri = fp.fileURL;
+  var uri = fp.fileURL.QueryInterface(Components.interfaces.nsIURL);
   uri.query = "type=application/x-message-display";
 
   window.openDialog( "chrome://messenger/content/messageWindow.xul", "_blank", "all,chrome,dialog=no,status,toolbar", uri, null, null );