One thing that annoys me about firefox's total cookie protection is that I offer some 3rd party embeds. What I did on those is I set a cookie, and probed for it

One thing that annoys me about firefox's total cookie protection is that I offer some 3rd party embeds. What I did on those is I set a cookie, and probed for its existance to check if the user has third party cookies disabled. Then if they do, it displays things for the case where it's not known whether or not the user is logged in to the service, rather than as if they're definitely not logged in. This worked fine, but now that firefox just containerizes third party resources rather than actually blocking the cookies, so there's no longer a way to detect that the actual site cookies just aren't being delivered in a third party context, rather than not present without user agent sniffing.