Internet Explorer 6 doesn't support the abbr element. Simply put, IE 6 doesn't recognize this element as a node of the DOM tree. To make IE 6 support this element or, more precisely, to mimic the support to this element, we have to manually create it within the DOM structure. This can be done at the very beginning of our page, like so:
<head>
<!--[if lte IE 6]>
<script type="text/javascript">document.createElement('abbr');</script>
<![endif]-->
</head>
Now we can select this element with CSS and apply the desired styles to it.
A very useful trick.