Firefox has terrible sandboxing and this is largely what makes it so far behind in security.
The following is written by security expert Daniel Micay who is the developer behind GrapheneOS, a hardened version of Android that provides Google with many of the upstream security enhancements that eventually land in AOSP:
Source:
https://grapheneos.org/usage (command+f "firefox")
Most of that is focused on the mobile implantation but I've bolded towards the end where the desktop version is specifically mentioned.
It all paints a pretty bad picture of Firefox security when they're so sloppy they don't even implement sandboxing APIs provided by the OS.
The fact it's especially bad on Linux also leads me to wonder if it's equally as bad on macOS given they're both Unix systems. I'm sure they share at least some code. But I've not done enough digging to make any definitive statements on that.
Either way I would definitely go for a Chromium based browser over Firefox myself. I agree entirely Chrome is the worst for privacy. That's why I mentioned Brave and Vivaldi. Awaiting ARM builds for those.