here is something interesting:

https://video.twimg.com/amplify_video/1396952987709235202/vid/1280x720/AK3jGofOt3JGwpJ5.mp4?tag=14

Once again you did not answer the question but instead place a ad video for FF.

Something I find interesting is that FF for android no long has about:config, The Desktop version as of 88.01 started in Jan-2021 no longer has built in feedback.

These kinds of studies: About Studies ?

I have a secret list of the live studies on this page: https://www.jeffersonscher.com/sumo/shield.php

IMPORTANT: I do not research what they are or answer questions about them. I look at the list if a bunch of people report something unusual happening to see whether there might be an explanation for the pattern.

It seems that you have to register to receive studies. But what happens to firefox users that leave the default enabled studies settings without registering?

It seems that you have to register to receive studies.

Why do you say that?

By default FF has install and run studies all selected. If you are required to register to participate why are those values selected?

By default FF has install and run studies all selected. If you are required to register to participate why are those values selected?

Why do you think you need to register to participate?

Your post suggested secret list. I was not able to get a handle on the studies and there appears to be no version on FF if a study is some how implemented.

You can see what studies your Firefox is participating in now and has participated in before by loading the about:studies page. See: About Studies. You don't need my list for that, only if you want to see all the active studies.