Disable directory listings in openfire

I'm using OpenFire 3.8.2. How can I disable directory listings in the admin web console? E.g. when I navigate to

http://myserver:9090/images/

I get a full listing of the files in /opt/openfire/plugins/admin/webapp/images on the server. I would like to disable that functionality. Is there a way to do that?

I tried searching for ways to do that in Jetty, which it seems is what runs under the hood for openfire's web server, but all the documentation I could find used config files that were significantly different from the ones openfire uses.