<!-- #################################################### -->

function equalColumns(){
  var l = document.getElementById('content_left');
  var r = document.getElementById('content_right');
  if (r.offsetHeight >= l.offsetHeight) {
        l.style.height = (r.offsetHeight + 16) + "px";
        r.style.height = r.offsetHeight + "px";
  } else {
        r.style.height = (l.offsetHeight - 16) + "px";
        l.style.height = l.offsetHeight + "px";
  }
}

<!-- #################################################### -->