Firefox Add-on installation page

index.html

<script type="application/javascript">
<!--
function install (aEvent)
{
  for (var a = aEvent.target; a.href === undefined;) a = a.parentNode;
  var params = {
    "Foo": { URL: aEvent.target.href,
             IconURL: aEvent.target.getAttribute("iconURL"),
             Hash: aEvent.target.getAttribute("hash"),
             toString: function () { return this.URL; }
    }
  };
  InstallTrigger.install(params);

  return false;
}
-->
</script>

<a
  href="https://addons.mozilla.org/firefox/downloads/file/368252/google_redirects_fixer_tracking_remover-2.0.0-fx.xpi"
  iconURL="http://localhost/icon.png"
  hash="sha1:35a56e7421cb8712f6c48a2240e89192e73bd742"
  onclick="return install(event);">Install Extension!</a>