fxa/_dev/firebase/firebase.json

{
  "emulators": {
    "firestore": {
      "host": "0.0.0.0",
      "port": 9090
    },
    "pubsub": {
      "host": "0.0.0.0",
      "port": 8085
    },
    "ui": {
      "enabled": true,
      "host": "0.0.0.0",
      "port": 9299
    }
  }
}