index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://www.gstatic.com/firebasejs/4.9.1/firebase.js"></script>
    <script src="https://www.gstatic.com/firebasejs/4.9.0/firebase-auth.js"></script>
    <script src="https://www.gstatic.com/firebasejs/4.9.0/firebase-database.js"></script>
    <link type="text/css" rel="stylesheet" href="https://cdn.firebase.com/libs/firebaseui/2.5.1/firebaseui.css" />
</head>
<body>
    <button onclick = "facebookSignin()">Facebook Signin</button> 
    
    <h1>Welcome to My Awesome App</h1>
    <div id="firebaseui-auth-container"></div>
    <div id="loader">Loading...</div>

</body>
</html>
<script src="script.js">
        
</script>