> Browsers can't use the OS control implementations, because the demands of DOM/CSS simply can't be handled by those native implementations. But Firefox is trying to emulate the look and feel of the OS controls, using native theme drawing APIs when possible.
Then Wowfunhappy wrote: "I wonder if that applies even to Safari on Mac and iOS". It absolutely does, Firefox and Safari work the same way here. But you appeared to think you were contradicting us when you wrote "Some of them are native, if you don't style them."
I guess it boils down to what you mean by "Safari on macOS uses native controls." Drawing with NSButtonCell and the other theme APIs does not, in my view, warrant such a blanket statement. All of the interactive behaviour of buttons and other widgets is (re)implemented by Webkit/Gecko. Accessibility is reimplemented. Layout is reimplemented. It's only painting that uses NSButtonCell, and not all painting either (borders and background but not the text).
I would certainly never claim "Firefox on MacOS uses native controls" even though it works pretty much the same way as Safari.