text: function ok(what, msg) {
    postMessage({ event: msg, test: 'ok', a: what });
  }
  
  function is(a, b, msg) {
    postMessage({ event: msg, test: 'is', a: a, b: b });
  }
  
  self.onmessage = function onmessage(event) {
  
    // An XHR with system privileges will be able to do cross-site calls.
  
    const TEST_URL = "http://example.com/tests/content/base/test/test_XHR_system.html";
    is(location.hostname, "mochi.test", "hostname");
  
    var xhr = new XMLHttpRequest({mozSystem: true});
    is(xhr.mozSystem, true, ".mozSystem == true");
    xhr.open("GET", TEST_URL);
    xhr.onload = function onload() {
      is(xhr.status, 200);
      ok(xhr.responseText != null);
      ok(xhr.responseText.length);
      postMessage({test: "finish"});
    };
    xhr.onerror = function onerror() {
      ok(false, "Got an error event!");
      postMessage({test: "finish"});
    }
    xhr.send();
  };
  