Fix #13393. Avoid IE9 activeElement of death.

src/event.js

@@ -11,6 +11,12 @@ function returnFalse() {
 	return false;
 }
 
+function safeActiveElement() {
+	try {
+		return document.activeElement;
+	} catch ( err ) { }
+}
+
 /*
  * Helper functions for managing events -- not part of the public interface.
  * Props to Dean Edwards' addEvent library for many of the ideas.
@@ -522,7 +528,7 @@ jQuery.event = {
 		focus: {
 			// Fire native event if possible so blur/focus sequence is correct
 			trigger: function() {
-				if ( this !== document.activeElement && this.focus ) {
+				if ( this !== safeActiveElement() && this.focus ) {
 					this.focus();
 					return false;
 				}
@@ -531,7 +537,7 @@ jQuery.event = {
 		},
 		blur: {
 			trigger: function() {
-				if ( this === document.activeElement && this.blur ) {
+				if ( this === safeActiveElement() && this.blur ) {
 					this.blur();
 					return false;
 				}

test/data/event/focusElem.html

+<!doctype html>
+<html>
+<head>
+  <meta http-equiv="Content-type" content="text/html; charset=utf-8">
+  <title>.focus() (activeElement access #13393)</title>
+
+  <script src="../../jquery.js"></script>
+</head>
+<body>
+  <a href="#" id="frame-link"></a>
+  <script>
+    jQuery("#frame-link").focus();
+    window.parent.iframeCallback( true );
+  </script>
+</body>
+</html>
\ No newline at end of file

test/unit/event.js

@@ -2416,6 +2416,11 @@ testIframeWithCallback( "jQuery.ready promise", "event/promiseReady.html", funct
 	ok( isOk, "$.when( $.ready ) works" );
 });
 
+testIframeWithCallback( "Focusing iframe element", "event/focusElem.html", function( isOk ) {
+	expect(1);
+	ok( isOk, "Focused an element in an iframe" );
+});
+
 // need PHP here to make the incepted IFRAME hang
 if ( hasPHP ) {
 	testIframeWithCallback( "jQuery.ready synchronous load with long loading subresources", "event/syncReady.html", function( isOk ) {