But then the answer is not "These things" and let the FF devs deal with the fallout. The answer would be "This is what you can do and you'll see quite a few odd results. Ask _me_ when you have questions and I'll explain as good as I can.".

I have quite a few of these switches on. First party isolation for example breaks the paypal payment flow on some, but not all, shops. It also breaks quite a few pages that recognize it as an adblocker. I know what to do if that happens, but I would never just recommend enabling that switch.