The DiscussionTools discussion parser (Parser.js) was originally written in JavaScript, then ported to PHP (CommentParser.php) after we decided we want to cache its results server-side. Now the code in Parser.js is mostly unused (except for a few functions, and except when using the dtdebug parameter), but it's still loaded on every page load.

It should be removed. dtdebug can probably be removed as it has been superseded by Special:DiscussionToolsDebug. Any useful functions should be moved to whatever uses them.