After reading lot of post I could not find a complete example how to send GCM push notifications using Pushsharp 4.0 with Firebase. Lot of examples with PushSharp are using the old Google cloud messaging, not Firebase and/or the old PushSharp version.
Does anyone have an example of a stable and working code for sending GCM push notifications using PushSharp 4.0 with Firebase ?
You can try this: https://github.com/Redth/PushSharp/issues/711
I haven't tried for myself but from the comments in above post, it appears people had success with PushSharp and Firebase with the suggested change.