Defining Firefox and IE Browser Response

 callback : function(options,success,result){
                var response = Ext.util.JSON.decode(result.responseText);

                if(response.success == true){

                    if(Ext.isIE){
                        messageBox(response.message, Ext.MessageBox.INFO);
                    }else{
                        successmessage(response.message);
                    }
                   
                }else{

                    if(Ext.isIE){
                        messageBox(response.errors.reason, Ext.MessageBox.ERROR);
                    }else{
                        errormessage(response.errors.reason);
                    }
                }
            }