title: ref.once() not called on Firebase
body: <p>I am puzzeled with the following issue. While making a little web page to see some data I have on Firebase, there is some place where I cannot access what I want.
  Of course I know there is something at this place on the server. Here is the code, it seems localRef.once() is never called.</p>
  
  <pre><code>var dbLocalURL = "https://atinytestapp.firebaseio.com/MyList/rc99/";
  var localRef = new Firebase(dbLocalURL);
  localRef.once("value", function(snapshot) {
      // WE NEVER COME HERE !!!!
      for (record in snapshot.val()) {
          document.write(record)
          var recordRef = new Firebase(dbLocalURL+record+"/");
          recordRef.once("value", function(rcdSnapshot) {
              var rcdData = rcdSnapshot.val();
              document.write(rcdData[“someKey”])
          })
      }
  }, function (errorObject) {
      // WE NEVER COME HERE !!!!
      console.log("The read failed: " + errorObject.code);
      document.write("The read failed: " + errorObject.code);
  });
  </code></pre>
  
  <p>My page accessing the data is working as it should about everywhere, except in one place with the above behaviour.
  Beside I have also checked that the URL I use is correct, by pasting it into a browser and seeing the data I expect.
  What can I be missing? I hope someone can give me a hint.</p>