I have an Add This button on my page in the footer and when I view in firefox it displays fine but in any other browser it goes onto two lines. How can I fix it?

<!-- AddThis Button BEGIN -->
<div class="addthis_toolbox addthis_default_style " style="float:right; margin:3px;">
<a class="addthis_button_preferred_1"></a>
<a class="addthis_button_preferred_2"></a>
<a class="addthis_button_preferred_4"></a>
<a class="addthis_button_compact"></a>
<a class="addthis_counter addthis_bubble_style"></a>

<script type="text/javascript" src="http://s7.addthis.com/js/250/addthis_widget.js#pubid=xa-4df4622e28d18591"></script>
<!-- AddThis Button END -->

I do have a CSS style sheet attached to the page but with nothing for this div on it.