As of Firefox 95 this add-on is again working. Thanks!

This add-on was working up until around Firefox version 93 and then it stopped altogether. It's still non-functional in FF version 94. I've tried to contact the developer a number of times but have received no responses. I'd like to see this working once again.

Unparalleled service and response. The owner contacted me right away. I highly recommend this add on. It is the best out there.

Does the job, very straightforward. You just specify your desired BCC address(es) and the extension does his job, just like that!