Push notifications allow us to push data to installed apps on a person's OS and their browsers. This would need background tasks and an activation system to support it. These would only be available to "installed" apps. Feature page with more scope available here: https://wiki.mozilla.org/Services/Notifications/Push/API
k9o+ as this is a top level requirement.
Removing fx15 flag - neither client or server bits will make it to fx15.
As I said in bug 763198, work is ongoing on this but push notifications won't land in v1 so I'm not marking this as a basecamp blocker.