Index: src/wp-admin/css/common.css
===================================================================
--- src/wp-admin/css/common.css	(revision 36162)
+++ src/wp-admin/css/common.css	(working copy)
@@ -2064,8 +2064,9 @@
 	line-height: inherit;
 }
 
-/* contain floats */
-.nav-tab-wrapper:after {
+/* modern clearfix */
+.nav-tab-wrapper:after, /* Back-compat for plugins */
+.wp-clearfix:after {
 	content: "";
 	display: table;
 	clear: both;