function fontResize() {
//besser: http://www.unintentionallyblank.co.uk/2007/11/09/fontsizer-reloaded-changing-font-sizes-with-javascript/
  var bigger = document.getElementById("font_bigger");
  var smaller = document.getElementById("font_smaller");
  var fontSize = 1;
  bigger.onclick = function() {
    if (fontSize < 2) {
      fontSize += 0.1;
      document.body.style.fontSize = fontSize + "em";
    }
    if (fontSize >= 2) {
      this.className = "disabled";
    } else {
      this.className = "";
    }
    return false;
  }
  smaller.onclick = function() {
    if (fontSize > 0.8) {
      fontSize -= 0.1;
      document.body.style.fontSize = fontSize + "em";
    }
    if (fontSize <= 0.8) {
      this.className = "disabled";
    } else {
      this.className = "";
    }
    return false;
  }
}

window.onload = function() {
  fontResize();
}