Firefox can't parse json string in jquery ajax response
===

I am getting strange problem while trying to parse json string in jquery ajax response-

Here is my ajax code :

    $.ajax({
             type: "POST",
             url: "Save",
             data: {expiry:expiry,settings:settings}
          }).done(function( msg ) {
                        alert(msg);
    	                var obj  = jQuery.parseJSON(msg);
    			       if(obj.status == "done"){
    			        window.location = obj.redirect;
                             }			 
    	   });

On IE,Chrome and Safari i am getting json string in alert ,
but in case of Firefox

i am getting `[obj XMLDocument]` in alert

Here is FF console :

![enter image description here][1]

**obj is null** , but i can see the response json string in the console under text attribute

    responses=Object { xml=document, text="{"status":"done","redir...ippetImage\/s\/6abb68"}

Any Reason for this behavior ?
  [1]: http://i.stack.imgur.com/6rAgh.jpg