If you have been following events, you would realise the release of Openfire 3.9 caught me by surprise. I am still making changes to the jitsivideobridge plugin and certainly was not ready for an immediate release.
I will post a blog and write a document at some point. In the meantime please see
In general, openfire plugins that create an embedded web service with Jetty, always require a restart of Openfire after the plugin is installed. It should have been fixed, but it is way down on the priority list.