$('barre').observe('mouseover', function(event) {
  Event.stop(event);
});

var mouseOverHandler = function(event) {
  $('barrepopup').slideDown({duration: 0.5});
  $('barrebutton').stopObserving('mouseover', mouseOverHandler);
  document.observe('mouseover', mouseOutHandler);
  
}

var mouseOutHandler = function(event) {
  $('barrepopup').slideUp({duration: 0.5});
  $('barrebutton').observe('mouseover', mouseOverHandler);
  document.stopObserving('mouseover', mouseOutHandler);
}

$('barrebutton').observe('mouseover', mouseOverHandler);