It uses multiple aggregation services, each of which get only partial data for each event, such that no individual service can track you, even if they wanted to. Initially the two aggregators are run by Mozilla and ISRG - your privacy is at risk only if you think both are malicious and actively sharing all the data between each other to track you.

As the number of aggregators increases this gets better - as long as you trust at least one aggregators involved then your individual data remains untrackable.

Also, in general if you think Mozilla is likely to _actively_ lie to you to steal your data and track you, you're probably using the wrong browser in the first place and the aggregation service makes little difference.