My main peave using FF on macOS is full-screening it is a terrible experience - unlike Safari, etc, moving the mouse to the top of the screen causes all the chrome (tabs, URL bar, etc) to shift down (and reveal some useless gap). That's not normal behavior, and should have been fixed 5 years ago.
Also, once you use Safari tab groups + tab preview its hard to go back to FF.
Also, once you use Safari tab groups + tab preview its hard to go back to FF.