https://firestore.googleapis.com/google.firestore.v1.Firestore/Listen/channel?database=projects%2Fnext-audit-demo%2Fdatabases%2F(default)&VER=8&RID=33636&CVER=22&X-HTTP-Session-Id=gsessionid&%24httpHeaders=X-Goog-Api-Client%3Agl-js%2F%20fire%2F7.24.0__C

This URL has not been tested yet.