Correct use of firebase and @firebase npm packages

When I add a dependency to the firebase >9.0.0 package, npm install downloads both node_modules\ firebase and node_modules\ @firebase (without mentioning about it).

I know the @firebase is the scoped package.

I'm asking because

1. Only Firebase (Google) seems to do this, so why two packages?
2. Should one refer @firebase because the unofficial is dropped at some point?
3. The codebases look similar so there is a lot of duplicate code.
4. Update can break imports and change functionality, meaning is it now with or without @ and how should one know that, like:

import { firebaseApp } from "firebase";

import { getMessaging } from "@firebase/messaging";

import { initializeApp } from "firebase/app";