Comment by grumbelbart2

I never understood why visited websites and all their first and third party cookies are not isolated by default in browsers.

There are so few sites where I really need cross-site logins to work that an opt-in would be much more preferable.

Have all sites set cookies on whichever third party they want, but don't share those cookies over. Add an explicit "Do you really want foo.com to share data with bar.com?" if you really need to see those facebook comments on your news site.