I just sent out the first issue of the Birdfeeder newsletter with a product update for a sub-set of users. A few of my users were still on the old authentication method which relied on users having a browser extension installed. This is not the case any more and just logging in will upgrade an account to the new method in the background.
I realized that users don't really log in often, as they consume Birdfeeder content in their email inbox so I exported the email addresses of the affected users and sent out a newsletter.
You can read the newsletter here: https://twitter.com/tehwey/status/1549477848582275074