[Vuejs]-VueJS / VueFire : data empty array

I’m learning firebase, myself. But, FWIW:

From https://firebase.google.com/support/release-notes/js

Before 8.0.0

import * as firebase from ‘firebase/app’

After 8.0.0

import firebase from ‘firebase/app’

A sample app from SinghDigamber, using firebase 7.13.2,
@ https://github.com/SinghDigamber/vue-firebase-setup/blob/master/src/firebaseDatabase.js

shows:

import * as firebase from ‘firebase’;

(i.e., without ‘/app’) So, you should try:

import * as firebase from ‘firebase’

as your firebase version is < 8.0.0