Public Suffix List (PSL) is an initiative of Mozilla community volunteers to maintain a list of top-level domains (TLDs) and domains that should be treated as one to prevent the mixing of cookies between distinct domains. Apple introduced a new privacy feature in version 14.5 of iOS, iPadOS, and tvOS, which asks users to grant permission to apps or websites that track them. Facebook suggested this as a remedy for the privacy enhancements introduced by Apple’s App Tracking Transparency (ATT) framework.
Source: https://www.bleepingcomputer.com/news/security/mozilla-flooded-with-requests-after-apple-privacy-changes-hit-facebook/