If a Browser is not as secure as possible, it is not as private as possible.

That applies vice-versa as well. Privacy is NOT a derivative of security, as Graphene loonies and idiots like madaidan would have you believe. This is one of the fundamental charlatan deeds "security" shills do in FOSS/privacy communities.

If Tor Project prefers Firefox over Chromium as base, then that simply means Firefox is superior for purposes of privacy, security and anonymity. Tor Project has hundreds or thousands of professionals that would make people like Brad Spengler and Micay look like a joke, as happened in the mailing lists in 2019, which made Micay invent lies to satisfy his ego and fanboy itches. He believes blindly in Google like a fanboy, which is the reason everything he does happens to support, fund and promote Google.

I avoid using a phone for anything remotely serious, and prefer a computer with the most common screen resolution and hardware for it. It depends on many factors what other measures I take, and I use Tor and I2P.