avoid unnecessary HTML string building+parsing

js/dropdown.js

@@ -34,7 +34,10 @@
     if (!isActive) {
       if ('ontouchstart' in document.documentElement && !$parent.closest('.navbar-nav').length) {
         // if mobile we use a backdrop because click events don't delegate
-        $('<div class="dropdown-backdrop"/>').insertAfter($(this)).on('click', clearMenus)
+        $(document.createElement('div'))
+          .addClass('dropdown-backdrop')
+          .insertAfter($(this))
+          .on('click', clearMenus)
       }
 
       var relatedTarget = { relatedTarget: this }