Eh, that honestly doesn't sound too bad, but good callout. Here's their article about it, and the relevant snippet:

PPA does not involve websites tracking you. Instead, your browser is in control. This means strong privacy safeguards, including the option to not participate.

Privacy-preserving attribution works as follows:

1. Websites that show you ads can ask Firefox to remember these ads. When this happens, Firefox stores an “impression” which contains a little bit of information about the ad, including a destination website.
2. If you visit the destination website and do something that the website considers to be important enough to count (a “conversion”), that website can ask Firefox to generate a report. The destination website specifies what ads it is interested in.
3. Firefox creates a report based on what the website asks, but does not give the result to the website. Instead, Firefox encrypts the report and anonymously submits it using the Distributed Aggregation Protocol (DAP) to an “aggregation service”.
4. Your results are combined with many similar reports by the aggregation service. The destination website periodically receives a summary of the reports. The summary includes noise that provides differential privacy.

This approach has a lot of advantages over legacy attribution methods, which involve many companies learning a lot about what you do online.

PPA does not involve sending information about your browsing activities to anyone. This includes Mozilla and our DAP partner (ISRG). Advertisers only receive aggregate information that answers basic questions about the effectiveness of their advertising.

Absolutely disable it if you're still uncomfortable with that, but don't knee-jerk disable it because ads. I'm hopeful that this is good enough for advertisers so they can stop the intrusive spying. I'm not a big fan of my browser tracking this info, but maybe it's better on net than alternatives.