"No shady privacy policies or back doors for advertisers" proclaims the Firefox homepage, but that's no longer true in Firefox 128.
Less than a month after acquiring the AdTech company Anonym, Mozilla has added special software co-authored by Meta and built for the advertising industry directly to the latest release
The way it works is that individual browsers report their behavior to a data aggregation server (operated by Mozilla), then that server reports the aggregated data to an advertiser’s server. The “advertising network” only receives aggregated data with differential privacy, but the aggregation server still knows the behavior of individual browsers!
Explaination from the article: