function display_fr(){
    var currTabElem = document.getElementById("navlist").childNodes;
    document.getElementById("fr").style.display = 'block';
    document.getElementById("etr").style.display = 'none';
    document.getElementById("disable").style.background = '#000000';
    document.getElementById("current").style.background = '#F2F2F2';
  }
  function display_etr(){
    var currTabElem = document.getElementById("navlist").childNodes;
    document.getElementById("etr").style.display = 'block';
    document.getElementById("fr").style.display = 'none';
    document.getElementById("current").style.background = '#000000';
    document.getElementById("disable").style.background = '#F2F2F2';
  }