Safari does it, because otherwise Apple would lose on the store front, and Chrome adoption has literally turned the Web into ChromeOS anyway.
Firefox doesn't come with OS and hardware to keep it around.
Firefox doesn't come with OS and hardware to keep it around.
So they're very aggressive to introducing "app-like" APIs to Chrome even often at the expensive of user experience, performance and security.
As you said, their very goal is turning the web into ChromeOS. And the web is everywhere.
Honestly, that's NOT a good thing for the future of either the web or applications.