Honestly, as annoyed as I am that they removed that privateWindowSeparation config - it was just a limited easement anyway. Leaving a manual bypass in about:config is just for a small subgroup of advanced users, looking to actively dive into those UI...
Every single time Firefox gets an upgrade, I find out from it just hard-restarting my session and everything I was doing, and I get to play the fun game of finding out what feature they broke this time and if it is even fixable.Guess this one is goin...