My jenkins is running behind an apache server, my configuration is very simple and look like this one : https://wiki.jenkins-ci.org/display/JENKINS/Running+Jenkins+behind+Apache

The plugin doesn't work with this configuration because absolute URL are used into the javascript code, for example in html5-notification.js there is a

...new Ajax.Request('/html5-notifier-plugin/list')...

that refer in my case to http://<HOST>/html5-notifier-plugin/list, but the real list is at http://<HOST>/jenkins/html5-notifier-plugin/list

It might be a Jenkins way to get the server URL properly and inject it into js files or java generated js code.

Ludovic.