Have you thought about having the extension read all of the page, look for PGP encrypted message and automatically decrypt the message? It wouldn't be compute intensive if you optimized for a specific website. Also getting the submitted message and encrypting on the fly?
Also, have you thought about how this could work for phones?
That's how it works, just searches the page for the pgp messages. It checks for messages on DOM changes.
FireFox on mobile enables add-ons, so it would work on desktop or mobile if I wanted to do that. However, this was more of a proof of concept. It worked and works well with friends, but we no longer use it all that much.
Have you thought about having the extension read all of the page, look for PGP encrypted message and automatically decrypt the message? It wouldn't be compute intensive if you optimized for a specific website. Also getting the submitted message and encrypting on the fly?
Also, have you thought about how this could work for phones?