The add-on author usually provides steps to install any necessary file(s) for native messaging to work. Where did you find the steps related to that folder? I don't see them in the documentation: https://www.mailvelope.com/en/help

Also, you might need to create that folder yourself. I guess try that first.

See also:

• https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Native_manifests

jscher2000 said

The add-on author usually provides steps to install any necessary file(s) for native messaging to work. Where did you find the steps related to that folder? I don't see them in the documentation: https://www.mailvelope.com/en/help

Their documentation is very essential and doesn't mention GnuPG integration settings. Incidentally, yesterday I downloaded Keybase and it automatically created the folder I was looking for (which Mailvelope didn't). Unfortunately, I'm still unable to get it to work. After moving the appropriate json file (at least according to a GitHub discussion from last december) to the folder, Mailvelope still tells me "GnuPG is not available".