This might be true for any run-of-the-mill service, but I do give Mozilla upfront credit as an entity and Firefox's privacy-leading track record. I haven't read the fine print, but I would be very surprised if there wasn't a robust layer of privacy/anonymisation involved. (Side note: I think the future is in-browser LLM (a la Gemini Nano), so I suspect they will eventually move there.)

Also consider that Apple has the big pockets to build their own server hardware, to claim multiple layers of privacy - but also remember that when they first introduced "differential privacy" and claimed it would be totally anonymous, privacy researchers soon found out that Apple set the epsilon so low that even after a few requests to their service, the user could be de-anonymized.

source: "Apple has boasted of its use of a cutting-edge data science known as "differential privacy." Researchers say they're doing it wrong." https://www.wired.com/story/apple-differential-privacy-short...