Maybe users could install browser extensions, and coordinate to gather datasets of which ads are displayed to whom. Cross-correlating this with personal informa

Maybe users could install browser extensions, and coordinate to gather datasets of which ads are displayed to whom. Cross-correlating this with personal information on the users (volunteered to a trustworthy third party, vetted by EFF lawyers), you could make inferences as to what Google probably knows about which user. And may provide a service to warn the user, in a privacy-respecting way, and give advice as to how to avoid further privacy invasions. Ironically enough, it might be illegal to do this, since it would injure Google's corporate privacy ("trade secrets").