Firestore no está funcionando en las funciones de Netlify.

module.exports.handler = async function(event, context) {

const firebase=require("firebase/app");
require("firebase/firestore"); 

const firebaseConfig = {
  apiKey: oculto,
  authDomain: oculto,
  projectId: oculto,
  storageBucket: oculto,
  messagingSenderId: oculto,
  appId: 
};

// Inicializa Firebase
firebase.initializeApp(firebaseConfig);
const db = firebase.firestore();
let path = event.path.split('/').pop();
if(path==="hi"){
    return {
    statusCode: 200,
    body: '<h1 style="color:green;text-align:center">${path}</h1>'
    }
}
else{
    return {
    statusCode: 200,
    body: '<h1 style="color:green;text-align:center">${"contactar al administrador del sitio"}</h1>'
    }
}
}

El error es

{ "errorType":"TypeError", "errorMessage":"firebase.firestore no es una función", "trace":["TypeError: firebase.firestore is not a function", " at Runtime.module.exports.handler (/var/task/server/index.js:22:21)"," at Runtime.handleOnce (/var/runtime/Runtime.js:66:25)"]}