react-native-firebase/example/demo/index.android.js

import React, { Component } from 'react';
import {
  AppRegistry,
  StyleSheet,
  View
} from 'react-native';
import App from './app';

export default class demo extends Component {
  render () {
    return (
      <View style={styles.container}>
        <App />
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1
  }
});

AppRegistry.registerComponent('demo', () => demo);