The Tor Browser / file revision

 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 should be mochi.test");

   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();

 };