enter image description here

the code in the HTML file is:

<script src="https://www.gstatic.com/firebasejs/9.1.2/firebase-app.js"></script>
<script src="https://www.gstatic.com/firebasejs/9.1.2/firebase-database.js"></script>
<script src="firebase.js"></script> 

And the firebase.js has this code:

  // Import the functions you need from the SDKs you need
  // import { initializeApp } from "https://www.gstatic.com/firebasejs/9.1.2/firebase-app.js";
  // TODO: Add SDKs for Firebase products that you want to use
  // https://firebase.google.com/docs/web/setup#available-libraries

function initializeApp() {
  // Your web app's Firebase configuration
  const firebaseConfig = {
    apiKey: "XXXXXXXXXXXXXXXXXXXXX",
    authDomain: "coupon-finder-73300.firebaseapp.com",
    projectId: "coupon-finder-73300",
    storageBucket: "coupon-finder-73300.appspot.com",
    messagingSenderId: "432596469035",
    appId: "1:432596469035:web:54b907640f9065fc33b16e"
  };

  // Initialize Firebase
  const app = initializeApp(firebaseConfig);
  console.log(app);  
}

The folder is load unpacked in the chrome extension, and there it generates no error, but as shared in the image above when I browse that file in the browser it generates an error:

Uncaught SyntaxError: Unexpected token 'export'
firebase-database.js:1 Uncaught SyntaxError: Cannot use import statement outside a module

what step should I do to troubleshoot?