Tbh I didn't believe this was the case until I actually looked for myself... [1] this file shows the default value of the "private attribution" submission, which is set to true.
To play devil's advocate, Firefox *is* trying to be privacy-mindful in running this "experiment" [2], but it is disappointing to see them make the decision to portray it like this.
I notice that these threads seem like quite the shit-fest on Mozilla which I personally think is undeserved. If you read their article [3] on the topic, they blatantly describe it as an experiment, and state most of the things others have been saying throughout these threads. "Tracking is terrible for privacy, because it gives companies detailed information about what you do online." (This is their words.)
Mozilla's solution to this practice is to 1) NOT provide your personal information 2) ONLY provides the website/ad provider with a count (and probably some other meta info like user-agent) of how many users actually clicked your ad 3) does NOT generate and display individual reports but instead 4) encrypts these reports, aggregates them, then submits the report with "noise that provides differential privacy." [4]
This whole thing just sounds like an excuse to get angry at corporations for trying to track our every move and squeeze as much money out of us as possible. Yes, that's exactly what's happening, but Mozilla **IS** trying very hard to protect your individual privacy, whilst also creating these features to satisfy advertisers.
Haters gonna hate ¯\_(ツ)_/¯
[1]
https://searchfox.org/mozilla-central/source/modules/libpref/init/StaticPrefList.yaml#3273[2]
https://bugzilla.mozilla.org/show_bug.cgi?id=1901068[3]
https://support.mozilla.org/en-US/kb/privacy-preserving-attribution[4]
https://en.wikipedia.org/wiki/Differential_privacy