"'firebase' is not defined" error when using firebase.firestore.timestamp

I'm using firebase, authentication and storage without problems in my React app. However, when I tried to use the firebase timestamp, I'm getting "'firebase' is not defined" error.

How I use timestamp:

    const duedate = moment().add(1, 'd').toDate();
const timestamp = firebase.firestore.Timestamp.fromDate(duedate)

I have firebase etc. initialized in a different file. I tried all possible imports:

import firebase from 'firebase/compat/app;
import * as firebase from 'firebase/compat/app;
import firebase from 'admin/compat/app;

and many variations. Nothing seems to help.

I'm using the latest version of firebase. Do you have any idea on how to solve it please?

Edit: This is how I import Firebase in the firebase.js file:

import { initializeApp } from "firebase/app";
import { getFirestore } from "firebase/firestore";
import { getAuth } from "firebase/auth";
import { getStorage } from "firebase/storage";

const firebaseConfig = {

};

export const app = initializeApp(firebaseConfig);
export const db = getFirestore(app);
export const auth = getAuth(app);
export const storage = getStorage(app);

I found an answer after many trials and errors, maybe it helps another lost beginner.

The problem was that I needed to import all the below, and not just firebase, apart from the configuration that I've already been importing from my config file.
When importing only the first line below, it was still showing me the error 'firebase is not defined'.

import firebase from 'firebase/compat/app';
import 'firebase/compat/firestore';