When Execute My Website if i have to enter ID and Password in login page then press Enter Button They open New Window In (Fire Fox Browser) But they Work Properly in Internet Explore , Google...

<script language="javascript" type="text/javascript">
    //the purpose of this function is to allow the enter key to
    function doClick(buttonName, e) {
        var key;
        if (window.event)
            key = window.event.keyCode;     //IE
        else
            key = e.which;     //firefox
        if (key == 13) {
            var btn = document.getElementById(buttonName);
            if (btn != null) { //If we find the button click it
                btn.click();
                event.keyCode = 0
            }
        }
    }

</script>

protected void Page_Load(object sender, EventArgs e)
  {
     // if (!IsPostBack)
      if (!this.IsPostBack)
      {
          Control myLoginButton = Login1.FindControl("LoginButton");
          if (myLoginButton != null && myLoginButton is IButtonControl)
          {
              Login1.Attributes.Add("onKeyPress", "doClick('" + myLoginButton.ClientID + "',event)");
          }
      }
  }