Nowadays Jenkins declares only few mimetypes : https://github.com/jenkinsci/jenkins/blob/master/war/src/main/webapp/WEB-INF/web.xml
The issue is that the real list of mimetypes recognized depends a lot of the container used to host jenkins. There is a large list of choices managed by Tomcat but it is really poor for winstone and thus when we are browsing a workspace we may have various issues on files like PDF and co.