Index: /CKEditor/branches/prototype/_source/plugins/tab/plugin.js
===================================================================
--- /CKEditor/branches/prototype/_source/plugins/tab/plugin.js	(revision 2983)
+++ /CKEditor/branches/prototype/_source/plugins/tab/plugin.js	(revision 2984)
@@ -146,4 +146,7 @@
 			element = new CKEDITOR.dom.element( element );
 
+			if ( element.getComputedStyle( 'display' ) == 'none' || element.getComputedStyle( 'visibility' ) == 'hidden' )
+				continue;
+
 			if ( element.getTabIndex() === 0 )
 			{