Index: branches/5.3.x/core/admin_templates/languages/email_template_settings.tpl
===================================================================
diff -u -N -r15677 -r15902
--- branches/5.3.x/core/admin_templates/languages/email_template_settings.tpl	(.../email_template_settings.tpl)	(revision 15677)
+++ branches/5.3.x/core/admin_templates/languages/email_template_settings.tpl	(.../email_template_settings.tpl)	(revision 15902)
@@ -186,7 +186,7 @@
 	// enable all disabled controls before submit
 	Application.setHook('email-template:*',
 		function () {
-			$(':input:disabled').attr('disabled', '');
+			$(':input:disabled').prop('disabled', false);
 		}
 	)
 </script>