Index: src/wp-includes/js/wp-embed.js
===================================================================
--- src/wp-includes/js/wp-embed.js	(revision 35700)
+++ src/wp-includes/js/wp-embed.js	(working copy)
@@ -1,9 +1,15 @@
 (function ( window, document ) {
 	'use strict';
 
-	var supportedBrowser = ( document.querySelector && window.addEventListener ),
+	var supportedBrowser = false,
 		loaded = false;
 
+		if ( document.querySelector ) {
+			if ( window.addEventListener ) {
+				supportedBrowser = true;
+			}
+		}
+
 	window.wp = window.wp || {};
 
 	if ( !! window.wp.receiveEmbedMessage ) {
@@ -50,8 +56,10 @@
 				targetURL.href = data.value;
 
 				/* Only continue if link hostname matches iframe's hostname. */
-				if ( targetURL.host === sourceURL.host && document.activeElement === source ) {
-					window.top.location.href = data.value;
+				if ( targetURL.host === sourceURL.host ) {
+					if ( document.activeElement === source ) {
+						window.top.location.href = data.value;
+					}
 				}
 			}
 		}
@@ -85,10 +93,12 @@
 			}
 
 			/* Remove security attribute from iframes in IE10 and IE11. */
-			if ( ( isIE10 || isIE11 ) && !!source.getAttribute( 'security' ) ) {
-				iframeClone = source.cloneNode( true );
-				iframeClone.removeAttribute( 'security' );
-				source.parentNode.replaceChild( iframeClone, source );
+			if ( ( isIE10 || isIE11 ) ) {
+				if ( !!source.getAttribute( 'security' ) ) {
+					iframeClone = source.cloneNode( true );
+					iframeClone.removeAttribute( 'security' );
+					source.parentNode.replaceChild( iframeClone, source );
+				}
 			}
 		}
 	}