Use function top_httphead to include headers in pages.

htdocs/core/js/lib_head.js.php

@@ -39,7 +39,7 @@ session_cache_limiter(FALSE);
 require_once '../../main.inc.php';
 
 // Define javascript type
-header('Content-type: text/javascript; charset=UTF-8');
+top_httphead('text/javascript; charset=UTF-8');
 // Important: Following code is to avoid page request by browser and PHP CPU at each Dolibarr page access.
 if (empty($dolibarr_nocache)) header('Cache-Control: max-age=3600, public, must-revalidate');
 else header('Cache-Control: no-cache');