function getBrowserWidth(){
  if (window.innerWidth){
    return window.innerWidth;}  
  else if (document.documentElement && document.documentElement.clientWidth != 0){
    return document.documentElement.clientWidth;  }
  else if (document.body){return document.body.clientWidth;}    
    return 0;
}

function dynamicFontsize(){
  var browserWidth = getBrowserWidth();

  if (browserWidth < 700){
    changeFontsize("small");
  }
  if ((browserWidth >= 700) && (browserWidth <= 1250)){
    changeFontsize("medium");
  }
  if ((browserWidth >= 1250) && (browserWidth <= 1450)){
    changeFontsize("large");
  }
  if (browserWidth > 1450){
    changeFontsize("largest");
  }
}

function changeFontsize(fontsize){
  var i, a;
  for(i=0; (a = document.getElementsByTagName("link")[i]); i++){
    if(a.getAttribute("title") == fontsize){a.disabled = false;}
    else if(a.getAttribute("title") != "medium"){a.disabled = true;}
  }
}

function addEvent( obj, type, fn ){ 
  if (obj.addEventListener){ 
    obj.addEventListener( type, fn, false );
  }
  else if (obj.attachEvent){ 
    obj["e"+type+fn] = fn; 
    obj[type+fn] = function(){ obj["e"+type+fn]( window.event ); } 
    obj.attachEvent( "on"+type, obj[type+fn] ); 
  } 
} 
  
addEvent(window, 'load', dynamicFontsize);
addEvent(window, 'resize', dynamicFontsize);