In my Firefox 52.5.1 under a current CentOS 7, there is no about:studies. Either "studies" has been newly removed (Firefox updated yesterday, I think?) or about:studies is new or Firefox Studies has been included by default after the 52 series. Perhaps its just me, but I still think of post-52 Firefox as "new".
It's nonetheless not obvious to me why you were downvoted; I don't know if someone else was annoyed at your definition of "new" or whether there were other dubious claims in your comment. Perhaps privacy advocates are just too exhausted and cranky to explain themselves again.
Just as another data point, I'm on 56.0, and while the option is there, it is default not enabled. So, it looks like something changed in the move to Quantum.
It's nonetheless not obvious to me why you were downvoted; I don't know if someone else was annoyed at your definition of "new" or whether there were other dubious claims in your comment. Perhaps privacy advocates are just too exhausted and cranky to explain themselves again.