<a id="myFeed">The feed:// URL</a>

<script>
    if (window.layoutTestController)
        layoutTestController.setCustomPolicyDelegate(true);

    var myFeed = document.getElementById("myFeed");
    myFeed.href = "feed://127.0.0.1:" + document.location.port + "/security/resources/feed.xml";

    var evt = document.createEvent("MouseEvents");
    evt.initMouseEvent("click", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
    myFeed.dispatchEvent(evt);

    if (window.layoutTestController)
        layoutTestController.setCustomPolicyDelegate(false);
</script>