I'm new to programming Actions for Google Home/Assistant.
I have been using the Inline-Editor under Fulfilment lately and it works fine. Now I want to start using the Firebase DB.
As it says const functions = require('firebase-functions'); in the first lines of the Inline Editor I am assuming, that the Database is ready to use?
If so, how do I access it?
Although Dialogflow uses Firebase Functions to let you do inline code-editing, it doesn't sound like it is a full-fledged Firebase environment. There may be APIs on the back-end that are not setup.
The Dialogflow In-line Fulfillment is meant for simple logic testing and simple operations.
Fortunately - it isn't difficult to take that code and expand it into code that you write... and still host on Firebase Functions! See https://firebase.google.com/docs/functions/get-started for the tools you'll need to install to get started.
For a more extensive tutorial about writing Firebase Functions that work with Dialogflow and getting started with Firebase Functions, you can take a look at the codelab from Google at https://codelabs.developers.google.com/codelabs/assistant-dialogflow-nodejs/index.html