function theflashxt()
{
 if (a==0)
 {
  document.getElementById("theflashxt").innerHTML += "<embed src='/exit.swf' autostart='true' width='0' height='0'></embed>";
  alert("Merci de votre visite !");
 }
}

function startxt()
{
 if (navigator.userAgent.indexOf("Firefox") != -1) { theflashxt(); }
 else { eval("window.attachEvent('onunload',theflashxt);"); }
}

window.onunload = startxt;