[Firebase + Angular] When exactly is data loaded from Firebase?

I have some questions about how $firebase works.

Taking this super simple controller for example:

var app = angular.module("app", ['firebase']);


app.constant('FBURL', 'https://groupstest.firebaseio.com/');


app.controller("ApplicationController", [
   '$scope',
   '$firebase',
   'FBURL',
   function($scope, $firebase, FBURL) {
     var groups = $firebase(new Firebase(FBURL + 'groups'));
     $scope.groups = groups;
   }]);

Given that the above code is all I need in order to be able to iterate over
the groups in my Firebase DB using ng-repeat....


    1. Does doing: $firebase(new Firebase(FBURL + 'groups')).$child("2"); load
    all groups before accessing the child or does it only load data associated
    with the child node?
    2. What about: $firebase(new Firebase(FBURL + 'groups/2')); Is that the
    same or different to the line above?

Finally as a bonus question ;-) .... If I do this:

$firebase(new Firebase(FBURL + 'groups/1'));
$firebase(new Firebase(FBURL + 'groups/2'));
$firebase(new Firebase(FBURL + 'groups/3'));

How many Firebase connections do I now have open? 1 or 3? Is this an
inefficient thing to do?

It's possible I'm not fully understanding how websockets works so my
apologies if that is the case. I'm used to a more traditional HTTP API
setup.