I have spent ~10 years using Firefox daily, tweaking the config and getting the addons set up the way I want. I was a professional web developer for most of those years.
This is the first I have heard of Firefox changing my config settings invisibly in the background. This is obscene. Who on earth thought this was a good idea? The security ramifications are limitless.
I understand all too well that most companies have decided to start A/B testing things on subsets of users, but that doesn't mean you should force that mode of thinking into everything. What a horrible decision. I don't recall ever seeing any news or notifications or checkboxes about studies or "Normandy" at any point.
Are there some other good open source alternatives to Firefox? I remember hearing about Brave but also that it was tied into some cryptocoin nonsense, so I'm not sure what else to look at.