How does Firebases anonymous authentication generate a UID?

Question

Is this based on the clients machine or browser or something else?

For example if I logged in anonymously using Chrome, would the same UID be used in Firefox on the same machine?

Answer 1

From the Firebase documentation on anonymous authentication:

Each time you login a user anonymously, a new, unique user ID will be generated, and your Firebase reference will be authenticated using these new credentials.

So each of the browsers (in your example) becomes a different user.