Now on Ubuntu "Jammy" with firefox 101.0.1. Also the new version 4.6.0 does not work. It can be installed, but is not detected by mail applications. The browser console shows

ExtensionError: No such native application gpgmejson



Just does not work, Ubuntu Impish, FF 100.0.1.

I actually never succeeded in installing this addon with firefox. Sad story.