function impressum() {
  var imp, leftpos, toppos;
  leftpos = (screen.width-350)/2;
  toppos = (screen.height-450)/2;
  imp = window.open("/impressum.fa-fo","Das Fa-Fo :: Impressum","width=400,height=360,top="+toppos+",left="+leftpos);
  imp.focus();
}