Likewise, I’m certain I was not able to access Firebase at that time.
Whether it was this cause or any other cause, the result was the same. Something in Thunkable servers did not allow the process to complete. Why, I don’t know.
The answer given was not complete nor precise. It only gave examples and to be honest, I don’t know where Firebase components fit.
I’ve pinged the engineering team and am waiting on a response! 
[Update]
Thanks for the great query here! It’s been confirmed by @paulmw
Thunkable apps implement a Firebase SDK to make calls directly to Firebase for both sign-in/sign-up blocks, cloud variables, and purple Firebase blocks (snapToPlace)
@jared please let us know, since you are a staff member, if exists any plans for now or for sometime in the future to “open” the Firebase Connection Settings @ runtime…
This isn’t possible at the moment. My approach here, until something changes on our platform, would be to harness a service like xano to make these api calls on the backend for you and to return data to the device.
You could upload service keys and access your users data from the cloud. It is likely more secure than storing service keys on a device that may get found by an unwanted intruder.
You could get a jwt using the service key and hit up the Firebase API’s directly as such.