Index: src/wp-includes/js/wp-a11y.js
===================================================================
--- src/wp-includes/js/wp-a11y.js	(revision 33596)
+++ src/wp-includes/js/wp-a11y.js	(working copy)
@@ -41,6 +41,10 @@
 		ariaLive = ariaLive || 'polite';
 		role = 'assertive' === ariaLive ? 'alert' : 'status';
 
+		if ( null !== window.frameElement ) {
+			return;
+		}
+
 		var $container = $( '<div>', {
 			'id': 'wp-a11y-speak-' + ariaLive,
 			'role': role,