'alarm' message handler issue

mozAlarms.js

(function() {
  'use strict';

  var received = false;

  navigator.mozSetMessageHandler('alarm', function(ev) {
    received = true;
    console.log('message handled ->', JSON.stringify(ev));
  });

  navigator.mozAlarms.add(Date.now() + 1000, 'ignoreTimezone', {
    testData: 42
  });

  var start = Date.now(), limit = start + 2000;

  var loop = function() {
    var req = navigator.mozAlarms.getAll();
    req.onsuccess = function(ev) {
      var cur = Date.now();
      console.log('at ', (cur - start), ' alarms: ',
        JSON.stringify(req.result), 'handled?', received);
      if (cur < limit) {
        setTimeout(loop, 100);
      }
    }
  };
  loop();
})(this);