I haven't been able to find any documentation of this, other than "we acquired Anonym, which claims to send the data to trusted execution environments".

They've been working on it since long before Anonym. First three links from my search:

https://www.mozilla.org/en-US/advertising/

https://www.mozilla.org/en-US/foundation/annualreport/2024/a...

https://www.mozilla.org/en-US/advertising/principles/

I'm sure the internet police's thorough investigation into themselves has shown they are doing nothing wrong.

I don't know what that's based on or means, but they do have the mission of protecting privacy and this would be a core contribution to that:

https://www.mozilla.org/en-US/advertising/