'updateCurrentUser failed: First argument "user" must be an instance of Firebase User or null.' when running in Firebase Hosting

Hi - I'm not sure if this is a bug report for FirebaseUI-web-react of FirebaseUI-web; I suspect this is the correct place but please tell me if not.

I'm running my app in Firebase Hosting, and I'm linking the magic/reserved URLs that autoconfigure firebase (``)

Later, when `` is mounted, I get this warn on the console:

> Warning: Firebase is already defined in the global scope. Please make sure Firebase library is only loaded once.

This warning is there because `window.firebase` is defined (it was defined from in the _init.js_ loaded from the reserved URL).

I understand this is because I have a "version" of firebase loaded from the CDN and another "version" of firebase loaded from NPM (from a firebaseui dependency).

I would ignore this warning (since I made sure I'm loading the same version of Firebase from the CDN and from npm) but after logging in using GOOGLE_AUTH as provider, I get:

> updateCurrentUser failed: First argument "user" must be an instance of Firebase User or null. Dismiss

and in [my experience this is related to the previous warning](https://github.com/firebase/firebaseui-web/issues/536#issuecomment-451788176).

So, my question would be: what's the correct way to use firebaseui-web-react when I'm running in the Firebase Hosting thus using Firebase from the CDN and not NPM.

thanks

Bắt đầu bằng cách tái hiện sự cố trên Firebase Hosting với script dành riêng /__/firebase/init.js và component StyledFirebaseAuth bằng cách sử dụng firebase.auth(). Kiểm tra cách instance Firebase từ CDN tương tác với dependency FirebaseUI được tải qua npm. Được xem là hoàn thành khi đã xác lập và lập tài liệu cho một thiết lập được hỗ trợ, tránh được cả cảnh báo duplicate-global lẫn lỗi updateCurrentUser.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.