Javascript issue on IE

Question

I have added the social links in my html page. When I added, the top nav of my pages is gone. Tats appeared in firefox but not in IE. Any one help me how can i resolve tis?

Here is the code i used.

<a class="addthis_button" href="http://www.addthis.com/bookmark.php?v=250&amp;username=xa-4b9a190d10b004d6"&gt;
    <img src="http://s7.addthis.com/static/btn/v2/lg-share-en.gif" width="125" height="16" alt="Bookmark and Share" style="border:0"/>
</a>
<script type="text/javascript" src="http://s7.addthis.com/js/250/addthis_widget.js#username=xa-4b9a190d10b004d6"&gt;&lt;/script&gt;