I dont know if my case is valid for you but my extension was approved with this allow domain list:
https://firestore.googleapis.com/google.firestore.v1.Firestore/Listen/channel?database=projects/xxxxxxxxxx
https://us-xxxxxxxxxx.cloudfunctions.net
https://api-xxxxxxxxxx.appspot.com
https://xxxxxxxxxx.firebaseio.com
wss://xxxxxxxxxx.firebaseio.com