No need to use the conditional comment for binding the onunload event in IE.

src/event.js

@@ -882,8 +882,8 @@ jQuery.each( ("blur focus load resize scroll unload click dblclick " +
 // Window isn't included so as not to unbind existing unload events
 // More info:
 //  - http://isaacschlueter.com/2006/10/msie-memory-leaks/
-/*@cc_on
-window.attachEvent("onunload", function() {
+if ( window.attachEvent ) {
+	window.attachEvent("onunload", function() {
 		for ( var id in jQuery.cache ) {
 			if ( jQuery.cache[ id ].handle ) {
 				// Try/Catch is to handle iframes being unloaded, see #4280
@@ -892,5 +892,5 @@ window.attachEvent("onunload", function() {
 				} catch(e) {}
 			}
 		}
-});
-@*/
+	});
+}