function centerPopup (url, target, paramsStr) {
  var pairs = paramsStr.toLowerCase().split(',');
  var new_pairs = [];
  var pair = [];
  var prop = '';
  var val = '';

  for (var i = 0; i < pairs.length; i++) {
    pair = pairs[i].split('=');
    if (pair.length != 2) continue;

    prop = pair[0].replace(/^\s*/, "").replace(/\s*$/, "");
    if (prop == '' || prop == 'left' || prop == 'top') continue;

    val = pair[1].replace(/^\s*/, "").replace(/\s*$/, "");
    if (val == '') continue;

    new_pairs.push(prop + '=' + val);

    if (prop == 'width') new_pairs.push('left=' + (screen.availWidth / 2 - val / 2));
    if (prop == 'height') new_pairs.push('top=' + (screen.availHeight / 2 - val / 2 - 40));
  }

  return window.open(url, target, new_pairs.join(','));
}