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;
 				}