Application developers choose to integrate Firebase — it was not added by Google. The question is, why are they doing it. I can think of two possible reasons:
Firebase push services are more reliable than the method which is employed by the F-Droid builds (?)
…For that we have no explanation: is there some problem with ntfy? --This is the only relevant thing I could find in the Jami documentation:
“A DHT Proxy is used with mobile devices to save battery by avoiding synchronization. It is generally dhtproxy.jami.net but can be any DHT node with the REST API enabled. However, if the DHT proxy is using push notifications it will depend on another external service (Firebase or APN or a Unified Push instance). In this case, only the third one can be self-hosted.”
Firebase provides a feature called ‘Error Reporting’ that automatically collects & reports device-specific error logs
…in which case there are various alternatives that respect user privacy better. But even if privacy is no concern to the user, he is still compelled to guess which push service will meet his needs best.
What is the selection criteria here? Does one method use less energy? If so, how much? Which one should he choose, and why?