I think they mean desktop Firefox on a touchscreen laptop, rather than mobile Firefox. Personally, I can't imagine trying to pinch-zoom on a desktop, but maybe I'm just old.
They're talking about a gesture that's specific to the Macbook trackpad; namely, the implementation you see in Safari, which is not the typical browser 'zoom' function that increases the size of elements and reflows the page, but rather zooms in to show you a subset of the DOM canvas as rendered, like mobile browsers do. It is definitely a handy feature but to characterize it as a missing 'standard' functionality I don't think is fair. No desktop browser had this functionality until Safari ported it over from the mobile version a few releases back as I recall, though Chrome has since copied it.
On Microsoft Surface in tablet mode I often want to pinch zoom. It works but it's limited to the discrete zoom levels that you see with Ctrl+ and Ctrl- so you don't get the smooth zoom you get on Chrome. I still prefer FF for a variety of other reasons so to me it's just a nitpick.