Ultimately, in terms of security, you're likely to find that both are similarly good.
What makes Firefox desirable over Chrome is that it's not beng developed by massive corporation that gets the majority of its profits selling user data and delivering targeted adverts.
The other thing that may act as a deciding factor is the "MacOS doesn't have viruses" effect. Wherein that because firefox has such a small userbase in comparison to chromium, it's far more profitable to find exploits in chromium.
They did back when that was the windows logo.