How To Disable Max And Min Button In Popup Form

I have a pop up window  how to disable the max and min button in the pop up form, this is my code,

function newwindow() {
             var paramVal = document.getElementById('txtUserName');
                  if (paramVal.value != "") {           
                       window.open('Forgotpassword.aspx', 'Forgotpassword', 'resizable = no, top=10, left=10, toolbar=no, width=620, height=480, status=no,   menubar=no');
                      return true;
                  } else  {
                      alert('Please Enter UserName');
                   } }