test.html

<embed type="application/x-jsgrowl" id="growl" hidden="true" />
<script>
  var growl = document.getElementById('growl');
  growl.register("JSGrowl test", "https://lh3.googleusercontent.com/eK1rTlFt1UfrUSoXFIh_phO7VwbFIRDbk-GvTf0vzPnm-VqEKELp575F5mWmCBk_zeGFXk2z=s128-e365-h128");
</script>
<a href="javascript:growl.notify('hi', 'hello with icon', 'http://lh6.googleusercontent.com/Y1OVGZMgnWeGpun6aGgoWfWcw3ZnrGpQdhIe90e_kWlDhAeZXn3Hk7Vyyi74FxmQodAMz5Klb7LgtQ=s256-c');" >icon</a>
<a href="javascript:growl.notify('hi', 'hello without icon');" >no icon</a>