Index: src/wp-admin/js/customize-controls.js
===================================================================
--- src/wp-admin/js/customize-controls.js	(revision 33526)
+++ src/wp-admin/js/customize-controls.js	(working copy)
@@ -3041,7 +3041,7 @@
 			return;
 		}
 
-		var parent, topFocus,
+		var parent,
 			body = $( document.body ),
 			overlay = body.children( '.wp-full-overlay' ),
 			title = $( '#customize-info .panel-title.site-title' ),
@@ -3555,13 +3555,6 @@
 
 		api.trigger( 'ready' );
 
-		// Make sure left column gets focus
-		topFocus = closeBtn;
-		topFocus.focus();
-		setTimeout(function () {
-			topFocus.focus();
-		}, 200);
-
 	});
 
 })( wp, jQuery );
Index: src/wp-includes/js/customize-loader.js
===================================================================
--- src/wp-includes/js/customize-loader.js	(revision 33526)
+++ src/wp-includes/js/customize-loader.js	(working copy)
@@ -232,6 +232,8 @@
 		 */
 		loaded: function() {
 			Loader.body.removeClass('customize-loading');
+			// Make sure the overlay gets focus.
+			Loader.iframe.contents().find( '.wp-full-overlay.expanded' ).attr( 'tabindex', 0 ).focus();
 		},
 
 		/**