<!-- The core Firebase JS SDK is always required and must be listed first -->
  <script src="https://www.gstatic.com/firebasejs/6.3.3/firebase-app.js"></script>

  <!-- TODO: Add SDKs for Firebase products that you want to use
      https://firebase.google.com/docs/web/setup#config-web-app -->
  <script src="https://www.gstatic.com/firebasejs//6.3.3/firebase-auth.js"></script>
  <script src="https://www.gstatic.com/firebasejs/6.3.3/firebase-firestore.js"></script>
  <script src="https://www.gstatic.com/firebasejs/6.3.3/firebase-storage.js"></script>
  <script src="https://www.gstatic.com/firebasejs/6.3.3/firebase-functions.js"></script>

  <script>
    // Your web app's Firebase configuration
    var firebaseConfig = {
      apiKey: "API_KEY",
      authDomain: "AUTH_DOMAIN",
      databaseURL: "DATABASE_URL",
      projectId: "PROJECT_ID",
      storageBucket: "STORAGE_BUCKET",
      messagingSenderId: "MESSAGING_SENDER_ID",
      appId: "APP_ID"
    };
    // Initialize Firebase
    firebase.initializeApp(firebaseConfig);
  </script>