As explained in the doc,
is the core Firebase SDK and is always required and must be listed first. But then you need to add the imports for the other SDKs you plan to use, like, for example:
<script src="https://www.gstatic.com/firebasejs/7.11.0/firebase-auth.js"></script> <script src="https://www.gstatic.com/firebasejs/7.11.0/firebase-firestore.js"></script>
Doing this way, all the Firebase SDKs will be imported, but it is not recommended for production apps, as stated in the doc.