Two updates to this thread.
Update 1: In this thread I complain Mozilla does not provide specific technical details about this feature. It turns out there *is* a document with the technical details, on Github:
https://github.com/mozilla/explainers/tree/main/ppa-experiment
It also explains (https://wiki.mozilla.org/Origin_Trials) which sites are participating in the feature.
I am linking this document because I believe the first five words do more to discredit what Mozilla is doing here than anything I could say:
"Mozilla is working with Meta"
@mcc
Simply put: 😬