The Tor Browser / file revision

 let port, es;

 let url = "https://example.com/browser/toolkit/components/social/test/browser/eventsource.resource";

 function ok(a, msg) {

   port.postMessage({topic: "eventSourceTest",

                    result: {ok: a, msg: msg}});

 }

 function is(a, b, msg) {

   port.postMessage({topic: "eventSourceTest",

                    result: {is: a, match: b, msg: msg}});

 }

 function esListener(e) {

   esListener.msg_ok = true;

 }

 function esOnmessage(e) {

   ok(true, "onmessage test");

   ok(esListener.msg_ok, "listener test");

   es.close();

   port.postMessage({topic: "pong"});

 }

 function doTest() {

   try {

     es = new EventSource(url);

     is(es.url, url, "eventsource.resource accessed", "we can create an eventsource instance");

     es.addEventListener('test-message', esListener, true);

     es.onmessage = esOnmessage;

   } catch (e) {}

   ok(!!es, "we can create an eventsource instance");

 }

 onconnect = function(e) {

   port = e.ports[0];

   port.onmessage = function(e) {

     if (e.data.topic == "ping") {

       doTest();

     }

   }

 }