Native notification support for Firefox is one of the most requested features of the Firefox community. The request is first posted by Firefox users almost four years back. Mozilla is finally adding native notification support for Firefox so that you can see all the push notifications from Firefox right in the Action Center. Microsoft introduced the Notification Center way back when Windows 10 is first released but Firefox didn't make use of it. In fact, it used its own notification system to show push notifications.
The native Notification support for Windows 10 is already available and you try it by installing Firefox Nightly build. According to the Bugzilla post, the new native notification support for Windows 10 is expected to launch for masses in Firefox 64.
Until then Moziall gradually rolls out the feature via Nightly builds and tests the feature via public testers so that there won't any hiccups when released to the actual public. As I said, you can install the Firefox Nightly build right now and see how the new native notification support works in Windows 10. Do keep in mind that the Nightly builds can be highly unstable and are not suited for production machines.
Since Firefox uses the native Windows 10 notification system, you can easily enable or disable Firefox notifications directly from the Windows 10 Settings app. That being said, for Nightly builds, as of now, there is no way to disable Firefox notifications. Mozilla didn't add the feature that enables users to control the notifications. Being Nightly builds, it is very much expected.
It's worth noting that when Firefox is using the native notification system in Windows 10, it won't show notifications using its own notification system. In fact, it doesn't make any sense to use two different notification systems.
Anyway, though it's late, it is very pleasing to see Mozilla finally adding native notification support for Windows 10. It just makes more sense to have all your notifications in one place and makes it a tad bit easy to control notifications.
Recently, Google also added native notification support for Chrome in Windows 10.