Unfortunately Firefox Relay uses Amazon Simple Email Service (Amazon SES). I despise Amazon and everything that they and Jeff Bezos stand for. Personally I do not do any business with Amazon and that includes Amazon AWS, and I wish that Firefox/Mozilla would find a better alternative for the core email service it is based on. Perhaps protonmail from Switzerland could provide this, which would be much better and ethically acceptable.

Regarding this add-on: The add-on works fine, but doesn't really add much useful functionality apart from being able to register an alias for relay addresses. The relay icon in any form field that accepts email is something that doesn't add anything for me, but it can be switched off. Instead of this add-on I prefer to use firefox lockwise for the usernames or email addreses and optionally the passwords.

Regarding Firefox Relay service: The number of 5 relay addresses is too little for my use case, also it would be good functionality that after switching off forwarding you'd be able to create a new relay address.

Some users have reported that some websites incorrectly assume these addresses to be temporary email. I believe this comes from the randomised hash in front of the @ sign. This could be circumvented by allowing manual entry of (part of) a username in a relay address.