title: Firebase returns snapshot but can't access value
body: <p>Peep is always returned from the function as undefined. Can someone point me to the problem? In the success function the snapshot is returned as expected. I think it's a scoping issue.</p>
  
  <pre><code>function getPerson( id ) {
  
      var ref = new Firebase( "https://foo.firebaseio.com/people/" + id ),
      peep;
  
      // Attach an asynchronous callback to read the data at our people reference
      ref.once( "value", function( snapshot ) {
          //success
          peep = snapshot;
  
      }, function ( errorObject ) {
          //error
          //console.log( "The read failed: " + errorObject.code );
      });
  
      return peep;
  
  }
  </code></pre>