I’d place Chrome and Firefox in a similar category with respect to privacy. Their derivatives are a different matter, as many seek to enhance privacy, and there are a few that do a decent job of it, I believe.
Firefox’s privacy policy lays it out (summarised here).
This study, albeit some years old now, cast Chrome, Firefox, Edge and Safari in a similar light. The fifth browser tested stands quite apart.
Our aim is to assess the privacy risks associated with this data exchange between a browser and its associated Google, Apple, Mozilla etc servers during general web browsing.
Chrome, Firefox, Safari and Edge all share details of web pages visited with backend servers. Additionally, Chrome, Firefox and Edge all share long-lived identifiers that can be used to link connections together and so potentially allow tracking over time. In the case of Edge these are device and hardware identifiers that are hard/impossible for users to change. On mobile devices, but not desktop devices, Firefox also shares device identifiers.
A similar report was concluded here, to reference Kuketz again. It likewise lumps Firefox in with behaviour consistent with Chrome and Edge.
With those reports, I acknowledge time has passed since they were conducted. If nothing else, they offer some near historical context.
Differentiating between security and privacy is of course a valid point too, and you prompted me to think on it since you raised the thought earlier @cactux. I’m not quite sure what it is you’re alluding to though.