> I thought cookies were locked per-domain since the invention of cookies
That is sort of what this mode breaks. Even if your web page on foo.com loads an image from bar.com, bar.com still cant set a cookie that it will get back next time you go to bar.com. So cookie's aren't "per-domain" any more, they are something much more complicated.
And yes, it breaks stuff .... so if for example, if you watch an embedded Youtube video on page A, youtube probably doesn't know its you and if you signed into Youtube previously as a suscriber to avoid ads guess what, you're now going to look anonymous and you'll get treated to ads even if you pay to not have them on Youtube normally.
That is sort of what this mode breaks. Even if your web page on foo.com loads an image from bar.com, bar.com still cant set a cookie that it will get back next time you go to bar.com. So cookie's aren't "per-domain" any more, they are something much more complicated.
And yes, it breaks stuff .... so if for example, if you watch an embedded Youtube video on page A, youtube probably doesn't know its you and if you signed into Youtube previously as a suscriber to avoid ads guess what, you're now going to look anonymous and you'll get treated to ads even if you pay to not have them on Youtube normally.