var inf = document.createElement("button");
    inf.setAttribute("style" , "position:fixed; top:4px; left:4px; width:1px; height:1px; border:none; background-color:#55f; opacity:0;");//-moz-opacityは3.5で廃止
    document.body.appendChild(inf);
    inf.focus();
    document.body.removeChild(inf);