GetRequest.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using BestHTTP;
using BestHTTP.ServerSentEvents;
using System;

public class GetRequest : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
         string firebaseHost = "https://fir-testdatabase-<REMOVED>.firebaseio.com/foo.json";

        Debug.Log("Opening Event Source");

        var eventSource = new EventSource(new Uri(firebaseHost), 1);
        // Start to connect to the server
        eventSource.OnMessage += OnMessage;
        eventSource.OnOpen += OnOpen;
        eventSource.Open();
    } 

    private void OnMessage(EventSource eventSource, Message message)
    {
        Debug.Log(string.Format("Message: <color=yellow>{0}</color>", message));
    }

    private void OnOpen(EventSource eventSource)
    {
        Debug.Log("EventSource.Open() callback");
    }
}