FastBoot unusable with Firebase projects

Hi.

I'm using FastBoot for a Firebase project and every time I pass in an object to their API, it ends up with this error

```
FirebaseError: Function addDoc() called with invalid data. Data must be an object, but it was: a custom Object object (found in document users/XqAOYqMtDfw0qXrDCMOM)
```

The code is as simple as

```javascript
const db = firebase.firestore();

db.collection('users').add({ name: 'Test User' });
```

I see a similar [issue](https://github.com/nuxt/nuxt.js/issues/6480) in Nuxt.js and I'm wondering if we're having the same case for FastBoot?

What I've tried so far is to disable the prototype extension but it doesn't seem to fix it.

Relevant links:
- https://github.com/nuxt/nuxt.js/issues/6480
- https://firebase.nuxtjs.org/community/faq/#firestore-using-array-contains-or-array-contains-any-does-not-work