Yes, I know. But they have plenty of old features that they support prefixed versions of, and people often enough use those without the corresponding standard

Yes, I know. But they have plenty of old features that they support prefixed versions of, and people often enough use those without the corresponding standard syntax. This means, of course, that Chrome can't drop their prefixed versions without breaking websites. As a result, Edge and Firefox are now implementing a bunch of prefixed stuff simply to be web compatible. For a view of what's needed in real-world terms for compat with the web nowadays, see https://compat.spec.whatwg.org/ https://compat.spec.whatwg.org/