OutputPage.php checks $wgUseAjax and some module specific configuration variables ($wgAjaxWatch, $wgEnableMWSuggest) before it includes javascript using AJAX. But $wgUseAjax isn't necessary, since these scripts don't use action=ajax any more. Instead it should check $wgEnableAPI (and $wgEnableWriteAPI for features that need it, like watching).
Both $wgEnableAPI and $wgEnableWriteAPIshould should also be checked together with $wgUseAJAXCategories.
Version: 1.20.x
Severity: enhancement