https://savannah.nongnu.org/projects/gcjwebplugin/

https://savannah.nongnu.org/forum/forum.php?forum_id=3991

Does anyone know if there are still security concerns with this version?

>From the Main page that shows the warning, but not the new version

http://www.nongnu.org/gcjwebplugin/news.html

WARNING:
The current version does not provide a security manager capable of handling Java (tm) applets. Applets have UNRESTRICTED access to your computer. This means they can do anything you can do, like deleting all your important data.