The article’s description of the feature is very inaccurate. The way it works is using secure two-party computation to aggregate data and apply DP server-side without Mozilla or the advertiser being able to see pre-aggregation data.
This has much better utility than applying DP client-side but still has similar privacy guarantees
All in all, I don't see why my own "privacy preserving" browser would snitch on me doing calls to an external server with aggregated data about my browsing history just to please advertisers...
Even if they pretend that data is "obfuscated" in some way...
This has much better utility than applying DP client-side but still has similar privacy guarantees