fyi, just tried to add a new addon to my 2 systems using legacy Mozilla addon Discovery and it failed to list any addons.
So, I decided to switch my development system to the new webthingsio image. After pulling the new webthingsio/gateway docker image it started up ok, and more importantly, addon Discovery once again worked.
Did not attempt to restart either of my mozilla docker images to see if that corrected legacy mozilla addon Discovery.
For me, I don’t care as I’m now running webthingsio which is probably the correct thing for others to do too…
Thank you for reporting, but this is expected. I’m afraid the Mozilla add-ons directory server was shut down at the end of 2020 along with the mozilla-iot.org tunnelling and update servers. This means that installing and updating add-ons will no longer work on WebThings Gateway 0.x as of 2021. I believe this was explained in an email sent out to all users of the mozilla-iot.org tunnelling service.
As you say, upgrading to 1.0 will use the new infrastructure at webthings.io, including the replacement add-ons directory.