Index: wp-admin/includes/meta-boxes.php
===================================================================
--- wp-admin/includes/meta-boxes.php	(revision 13812)
+++ wp-admin/includes/meta-boxes.php	(working copy)
@@ -608,7 +608,7 @@
  * @param object $link
  */
 function link_categories_meta_box($link) { ?>
-<ul id="category-tabs">
+<ul id="category-tabs" class="category-tabs">
 	<li class="tabs"><a href="#categories-all"><?php _e( 'All Categories' ); ?></a></li>
 	<li class="hide-if-no-js"><a href="#categories-pop"><?php _e( 'Most Used' ); ?></a></li>
 </ul>