https://www.propublica.org/article/facebook-blocks-ad-transparency-tools

>A number of organizations, including ProPublica, have developed tools to let the public see exactly how Facebook users are being targeted by advertisers.
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>Now, Facebook has quietly made changes to its site that stop those efforts.
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>ProPublica, Mozilla and Who Targets Me have all noticed their tools stopped working this month after Facebook inserted code in its website that blocks them.