Scrypt hash required for Firebase is not the Scrypt hash Auth0 has implemented

This has been asked in the community previously and erroneously assumed that Auth0 since now supports Scrypt algorithm - Firebase users can be seamlessly imported without requiring password changes.

Support for scrypt hash algorithm when importing users?

However, that is not the case Firebase uses a modified version of Scrypt

So seamless import in this manner is not possible. A possible solution is to use custom database and write your own Scrypt hash matching using now open sourced Firebase Scrypt library.