At the very least, Firefox's position on the similar <geolocation> element is positive.[0] I would assume their position for other permissions elements would be the same.
Apple and Firefox are running tests on the previous parts of this that recently came out (geolocation), so they will be doing the same with this one.
I seldom see visibility for any releases in popular browsers. The only time I notice any is if I don't use it for years, then get handed a work laptop that uses X browser. It's at least cool to see these docs even if I likely won't ever see/appreciate the element in use.