See the whitepaper[1] and blogs by Monica and Mozilla[2]. It works like a combination of safebrowsing and Disconnect. Basically they cache a list of "bad" URIs

See the whitepaper[1] and blogs by Monica and Mozilla[2]. It works like a combination of safebrowsing and Disconnect. Basically they cache a list of "bad" URIs and block them at request-time [1] https://kontaxis.github.io/trackingprotectionfirefox/resources/papers/trackingprotectionfirefox.w2sp15.pdf https://kontaxis.github.io/trackingprotectionfirefox/resourc... [2] monica-at-mozilla.blogspot.com