Are third-party cookies blocked?

The answer

Many current browsers block or partition them by default, but behaviour differs by browser, version, private mode and user settings, so there is no single answer. Partitioning keeps a separate cookie jar per top-level site, so an embed cannot recognise a person across sites. Test embedded features in several browsers with default settings and again with stricter tracking prevention, and design them so that a missing cookie degrades gracefully instead of failing silently.