indieconfig.js

(function () {
  if (window.parent !== window) {
    window.parent.postMessage(JSON.stringify({
      // The config of your endpoint
      reply: 'http://voxpelli.com/reply?u={url}'
    }), '*');
  }

  // Pick a way to invoke the registerProtocolHandler, through a submit handler in admin or something
  document.getElementById('confForm').addEventListener('submit', function (e) {
    e.preventDefault();
    window.navigator.registerProtocolHandler('web+indie', '/?url=%s', 'Indie Config');
  });
}());