Mozilla never did such a thing. The browsing history was never sent in any shape or form. As the journalistic article you quote states, Mozilla put in place the HumanWeb[1,2,3], which was a privacy preserving data collection which ensured record-unlinkability, hence no session or history. Anonymity was guaranteed and the framework was extensively tested by privacy researchers from both Cliqz and Mozilla.
Disclaimer: I worked at Cliqz.
The chosen excerpt omits the fact that it is predicated on the HumanWeb. In the technical papers above there is a more precise description on what and how was collected. There was no user tracking, session or history being sent as all data points are anonymous and record-unlinkable by the receiver. The vague language, required for a general audience journal, certainly does not help.
> Users who receive a version of Firefox with Cliqz will have their browsing activity sent to Cliqz servers, including the URLs of pages they visit.