Using setInterval() or setTimeout() in Javascript code and changing system time backward for example 1 hour causes browser (newest Safari)/ or engine (older version of QT WebKit) to freeze. Sample code: HTML: <p id="date"></p> JS: setInterval(SetTime, 1000); function SetTime() { document.getElementById('date').textContent=new Date(); } OR: (function loop() { document.getElementById('date').textContent=new Date(); setTimeout(loop, 1000); })(); StackOverflow question: http://stackoverflow.com/questions/23013324/webkit-setinterval-and-system-time-change