(function () {
    var overlay, lastCount, lastTime, timeoutFun;

    overlay = document.createElement('div');
    overlay.style.background = 'rgba(0, 0, 0, .7)';
    overlay.style.bottom = '0';
    overlay.style.color = '#fff';
    overlay.style.display = 'inline-block';
    overlay.style.fontFamily = 'Arial';
    overlay.style.fontSize = '10px';
    overlay.style.lineHeight = '12px';
    overlay.style.padding = '5px 8px';
    overlay.style.position = 'fixed';
    overlay.style.right = '0';
    overlay.style.zIndex = '1000000';
    overlay.innerHTML = 'FPS: -';
    document.body.appendChild(overlay);

    lastCount = window.mozPaintCount;
    lastTime = performance.now();

    timeoutFun = function () {
        var curCount, curTime;

        curCount = window.mozPaintCount;
        curTime = performance.now();
        overlay.innerHTML = 'FPS: ' + ((curCount - lastCount) / (curTime - lastTime) * 1000).toFixed(2);
        lastCount = curCount;
        lastTime = curTime;
        setTimeout(timeoutFun, 1000);
    };

    setTimeout(timeoutFun, 1000);
}())