Я следовал руководству (https://cloud.google.com/appengine/docs/standard/python/authenticating-users-firebase-appengine) для добавления Firebase в проект Google App Engine. Тем не менее, кнопки пользовательского интерфейса не отображаются; кто-то на Youtube сделал урок для Node.JS и кнопки интерфейса работали. Вот что я вижу после следования руководству: 
Там написано "Войти, но ничего не видно".
HTML
index.html
<!doctype html>
<!--
Copyright 2016 Google Inc. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
-->
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
<script src="https://www.gstatic.com/firebasejs/5.6.0/firebase-app.js"></script>
<script src="https://www.gstatic.com/firebasejs/5.6.0/firebase-auth.js"></script>
<script src="https://cdn.firebase.com/libs/firebaseui/3.4.1/firebaseui.js"></script>
<link type="text/css" rel="stylesheet" href="https://cdn.firebase.com/libs/firebaseui/3.4.1/firebaseui.css">
<link rel="stylesheet" type="text/css" href="style.css">
<script src="/main.js"></script>
<title>Firenotes</title>
</head>
<body>
<div id="logged-out">
<h1>Firenotes</h1>
<h3>Sign in to access your notebook</h3>
<div id="firebaseui-auth-container"></div>
</div>
<div id="logged-in">
<h1>Welcome, <span id="user"></span>!</h1>
<h3>Enter a note and save it to your personal notebook</h3>
<div id="form">
<form action="" method="post">
<div class="form-group">
<textarea id="note-content"></textarea>
</div>
<div class="form-group">
<button id="add-note">Save note</button>
<button id="sign-out">Sign out</button>
</div>
</form>
</div>
<div id="notes-container"></div>
</div>
</body>
</html>
suscessful rediredt good. html
<code><!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Sample FirebaseUI App</title>
<!-- The core Firebase JS SDK is always required and must be listed first -->
<script src="https://www.gstatic.com/firebasejs/7.9.1/firebase-app.js"></script>
<!-- TODO: Add SDKs for Firebase products that you want to use
https://firebase.google.com/docs/web/setup#available-libraries -->
<script src="https://www.gstatic.com/firebasejs/7.9.1/firebase-analytics.js"></script>
<script>
var firebaseConfig = {
apiKey: "AIzaSyDy38mpi5a_XI3BwZmxcaGG6AYfTp27yUM",
authDomain: "proj-noah-f1280.firebaseapp.com",
databaseURL: "https://proj-noah-f1280.firebaseio.com",
projectId: "proj-noah-f1280",
storageBucket: "proj-noah-f1280.appspot.com",
messagingSenderId: "584810873981",
appId: "1:584810873981:web:dc5305b0c20276f8bc9d14",
measurementId: "G-2CQTJ3ZHHV"
};
// Initialize Firebase
firebase.initializeApp(firebaseConfig);
firebase.analytics();
</script>
<script type="text/javascript">
initApp = function() {
firebase.auth().onAuthStateChanged(function(user) {
if (user) {
// User is signed in.
var displayName = user.displayName;
var email = user.email;
var emailVerified = user.emailVerified;
var photoURL = user.photoURL;
var uid = user.uid;
var phoneNumber = user.phoneNumber;
var providerData = user.providerData;
user.getIdToken().then(function(accessToken) {
document.getElementById('sign-in-status').textContent = 'Signed in';
document.getElementById('sign-in').textContent = 'Sign out';
document.getElementById('account-details').textContent = JSON.stringify({
displayName: displayName,
email: email,
emailVerified: emailVerified,
phoneNumber: phoneNumber,
photoURL: photoURL,
uid: uid,
accessToken: accessToken,
providerData: providerData
}, null, ' ');
});
} else {
// User is signed out.
document.getElementById('sign-in-status').textContent = 'Signed out';
document.getElementById('sign-in').textContent = 'Sign in';
document.getElementById('account-details').textContent = 'null';
}
}, function(error) {
console.log(error);
});
};
window.addEventListener('load', function() {
initApp();
});
</script>
</head>
<body>
<h1>Welcome to My Awesome App</h1>
<div id="sign-in-status"></div>
<div id="sign-in"></div>
<pre id="account-details"> Существует ли причина, по которой кнопки не отображаются?