Index: src/wp-includes/js/media-grid.js
===================================================================
--- src/wp-includes/js/media-grid.js	(revision 29256)
+++ src/wp-includes/js/media-grid.js	(working copy)
@@ -463,6 +463,7 @@
 
 				this.modal.on( 'open', function () {
 					$( 'body' ).on( 'keydown.media-modal', _.bind( self.keyEvent, self ) );
+					$( '.media-modal-close' ).blur();
 				} );
 
 				// Completely destroy the modal DOM element when closing it.