Browse to the URL https://wiki.jenkins-ci.org/display/JENKINS/Plugins

This URL should show a categorised list of Jenkins plugins. It is currently showing Java error messages against a number of the plugin headings. See screenshot attached.

(note: I appreciate this is the bug tracker for Jenkins itself and may not be the correct location to report errors on the Jenkins site, but I was unable to find anywhere else to report it; please feel free to move it to the correct location if necessary)