Call from AS3 to JS in a XULrunner application

Hi,
Is it possible to use the AS3 externalInterface to communicate with the JS in a xulrunner application? The same code works in a browser but doesn't work in the xulrunner environnment: the js function is not called. Is there something special to do?

simple sample code :

xul file:
<script type="application/javascript">
  function testExternalCall()
  {
    alert("Call from AS3 succeeded!");
  }
</script>

AS3:
m_external_call_test_button.addEventListener(MouseEvent.CLICK,callAS3toJS);

function callAS3toJS(e:MouseEvent):void
{
	ExternalInterface.call("testExternalCall");
}

Thanks in advance
Regards,