Need to confirm logout

Hi,

I'm trying configure a "confirm logout before exit" and the code below does the trick but when CKFinder sends a file for the user to download the alert also pops up. Is there any way to get round this?

var needToConfirm = true;
window.onbeforeunload = confirmExit;
function confirmExit()
{
    if (needToConfirm)
       return "Please use the log-out button.";
 }