Wow, thanks for the refresher that ethics != laws. I had accidentally completely forgotten that.
Now, back to the point. Nobody has made an ethical argument that Mozilla shouldn’t be pushing an extension that is a fork with a license preferable to them.
Well, these points were made in this thread and elsewhere, but in this case, pushing this extension instead of the original one prevents users to find the better version, and these users might even donate to the fork in the hope it will improve or to thank for the work, instead of donating to the original one, that really did the work and will be able to improve it.
Of course, this does not apply to every situation where there is a fork. In many situations, there is real work done in the fork, sometimes this work is even upstreamed.
> a fork with a license preferable to them
Both extensions have the same license (GPLv3), except the fork removed the original copyright notices from the original source code. This is probably not even allowed, let alone ethical.
Now, back to the point. Nobody has made an ethical argument that Mozilla shouldn’t be pushing an extension that is a fork with a license preferable to them.