Televangelist
Since firebase is a database, point a) is possible. For point b), it is also possible because that firebase allows users to monitor the changing of values.
But these features would not be easy to put into project directly. Maybe it needs some custom plugins for specific application.
My plan is to build social features (friend lists, private messages, message board, etc...) first, since these might be general for most multiplay games.
BTW, firebase is one of possible backend solutions, so it might have another better solution than firebase. Surveying these solutions is another important work, IMO.