No reason to double-bind the beforeunload event. Fixes #6113.

src/event.js

@@ -520,9 +520,8 @@ jQuery.event = {
 				if ( this.setInterval ) {
 					this.onbeforeunload = eventHandle;
 				}
-
-				return false;
 			},
+
 			teardown: function( namespaces, eventHandle ) {
 				if ( this.onbeforeunload === eventHandle ) {
 					this.onbeforeunload = null;