One solution is to do your routing on the client side with the $route service.
When a user authenticates through Firebase, save some record of this on the client, like in localstorage, some all-encompassing controller, or your own Angular service (my preferred option).
In your routing controller, if the user is authenticated, redirect to /some_page
, otherwise redirect to /login
and keep track of the $location where the user intended to go.
If, on the other hand, you want to route with your server, you could use the solution you linked to by having your server generate Firebase auth tokens.