I use FF, too, but I can see why someone wouldn't want to: It's just not a very good Mac app. Weird windowing and focus bugs in fullscreen mode. Keyboard shortcuts that randomly stop working. Zero scripting capabilities (it used to have the bare minimum, but Mozilla bizarrely ripped it out), and just poor integration in general. My system-wide shortcuts — the ones that are so important I've added them to every context menu on the system? That's a big nope because FF devs apparently think showing poxy extension icons is more important.
Google had the good sense to copy Safari's keyboard shortcuts in Chrome. Mozilla didn't.
The bookmark manager is straight out of Windows 95. Awful UX.
I do like Firefox, but it's just not up to snuff on macOS.