gecko-dev/dom/workers/test/worker_referrer.js

onmessage = function() {
  importScripts(["referrer.sjs?import"]);
  var xhr = new XMLHttpRequest();
  xhr.open("GET", "referrer.sjs?result", true);
  xhr.onload = function() {
    postMessage(xhr.responseText);
  };
  xhr.send();
};