Hope that helps I solved my problem building a server where the user register his token (unique identifier) to a database. There is also a PHP script for sending push notifications. You can find all of this here. I edited the PHP script to send a payload which contains :
["content-available"] = "1"
Is a Firebase Notification Received for a web app running on a mobile browser in the background?
Does that help From your stack trace, it looks like both calls are Firebase related. As such, try upgrading to the latest Firebase version 4.x to see if those go away. Please see this question if you may need some help when doing so.
Running a Node.JS background process for Twitter streaming API in Firebase
will be helpful for those in need Firebase Hosting can't run any code. Cloud Functions can run code, but not indefinitely, and only in response to defined triggers. Consider instead using multiple IFTTT with a Cloud Function as a webhook to receive tweets that meet some search criteria, as implemented in this project. You can set up multiple IFTTT applets if you need multiple queries to be aggregated in one place. This may be your best bet if you don't want to maintain your own server.
Google Firebase remote notifications not popping up when app is running in background