Requests for referrer are blocked when trying to sign in anonymously to Firebase
This helped for me:
console cloud google -> APIs & services -> credentials -> click on: browser key (auto created by firebase) -> application restrictions: none & API restrictions: don't restrict key.
Now your API won't block any requests. I hope this works!
It seems like you have set some referrer restrictions on your API key. You need to go to the Google Cloud Console and modify these restrictions on your API key.