I wish I had a good answer for this. It used to be the case that applets were exported into a single jar file, which could be signed and would work no problem. Now it's not clear which of the jar files actually needs to be signed, or if all of them do. I think there is also a problem with browsers caching jar files and reusing the cached version, which might not be signed. Best you can do is sign all of the jar files in the directory and try to run it on a fresh boot. I wish there was an easier way to deal with this...