you must use navigator.mozSetMessageHandler() https://developer.mozilla.org/en-US/docs/Web/API/Navigator.mozSetMessageHandler
if(navigator.mozSetMessageHandler) {
navigator.mozSetMessageHandler("alarm", function (alarm) {
// only launch a notification if the Alarm is of the right type for this app
if(alarm.data.task) {
// Create a notification when the alarm is due
new Notification("Your task " + alarm.data.task + " is now due!");
updateNotified(alarm.data.task);
}
});
}