"Cliqz uses different methods which should take care of removing sensitive information, before it's sent out from Firefox. Additionally, Cliqz does not create profiles of individual users and erases their IPs as soon as the data has been collected. The code of Cliqz is publicly accessible [open-source under MPLv2] [1] and a description of the used methods can be viewed here [in English, 2]."
[1] https://github.com/cliqz-oss/browser-core/blob/master/module...
[2] https://gist.github.com/solso/423a1104a9e3c1e3b8d7c9ca14e885...