This is weird & bad for so many reasons. But what I focus on is:
1. I believe, morally if not practically, this tracking is *worse* than the old 3rd-party cookies. This is because 3rd-party cookies were a legitimately useful tech that could be misused for ads. This tech is *designed* to benefit advertisers from word go, yet is installed on *your* computer, like Malware.
2. Firefox is *worse than Chrome* in their implementation of ad snitching, because Chrome enables it only after user consent.
Now to be clear, the disclosure Chrome provides to users is not *adequate*. Their wording of the "Ad Privacy" feature popup is highly disingenuous and the process to disable once notification is given is too complex and must be performed on a per-profile basis. But at least they *do it*, and to my knowledge don't track/send the data until the popup is displayed. Whereas Firefox just snuck this in in a software update, checked by default and you're probably learning about it now, on social media.