navigator.push is coming undefined in mozilla web IDE

I am using 2.2 mozilla OS simulator for push notification. When i am going to register APP with OS , its saying Push Notifications are not supported. while debugging its found that navigator.push is coming as undefined. Following is the sample code snippet.

var registerPush = document.querySelector('#register-push');

if (registerPush) {
    registerPush.onclick = function () {
        if (!navigator.push)
            return alert('Push notifications are not supported !');

        var request = navigator.push.register();

        request.onsuccess = function () {
            console.log(request.result);
        }

        request.onerror = function () {
            alert('Error getting a new endpoint !');
        }
    }
}