Apparently IE9 opens a background connection before sending the main HTTP request, blocking a single process server like HTTP::Server::PSGI.
via github.com
If anyone knows how to avoid background connections in IE9 (and probably Chrome incognito mode as well), let us know. Also if this is something you can fix on the HTTP::Server::PSGI side, we're happy to coordinate a patch.
Meanwhile, if you have issues developing with HTTP::Server::PSGI with IE9 or Chrome anonymous, you can use a very short timeout (like 1-2 sec), or use an event based web server like Twiggy or a forking web server like Starman or Starlet.