无法通过JavaScript发送多个同时通知

Question

我为Firefox编写了以下用户脚本：

window.onload = function start() {
  if (!Notification) {
    alert("Your browser doesn't support notifications");
    return;
  }

  foo();
}

function sendNotification(title, body, icon, linkToOpen) {
  if (Notification.permission !== "granted") {
    Notification.requestPermission();
  }

  var notification = new Notification(title, {
    icon: icon,
    body: body,
  });

  notification.onclick = function () {
    window.open(linkToOpen);
  }
}

function foo() {
  try {
    for (var i = 0; i < 1; ++i) { // here
      sendNotification(
        'Some title',
        'Some body',
        'http://cdn.akamai.steamstatic.com/steamcommunity/public/images/avatars/2f/2f6fd3197c8f38afc64d9309655362f23b46460a_full.jpg',
        'https://www.google.ru/'
      );
    }

    setTimeout(foo, 5000);
  } catch (ex) {
    alert(ex);
  }
}

如果我在此代码中将1更改为2，则根本不会发出通知。

为什么呢？我究竟做错了什么？我该如何解决？