function impressum() {
  var impressum = window.open("impressum.html", "impressum",
    "toolbar=no,status=no,menubar=no,scrollbars=no,resizable=no,width=450,height=480"); 
  impressum.focus();
}

function datenschutz() {
  var datenschutz = window.open("datenschutz.html", "datenschutz",
    "toolbar=no,status=no,menubar=no,scrollbars=yes,resizable=no,width=650,height=680"); 
  datenschutz.focus();
}

function openextra(url) {
  var extra = window.open(url, "extra","width=800,height=580");
  extra.focus();
}