just replace your app name and go.

firebase.json

{
  "firebase": "your-app-name-here",
  "public": "build",
  "ignore": [
    "firebase.json",
    "**/.*",
    "**/node_modules/**"
  ],
  "rewrites": [
    {
      "source": "**",
      "destination": "/index.html"
    }
  ],
  "headers": [
    {
      "source" : "**",
      "headers" : [
        {
          "key" : "Access-Control-Allow-Origin",
          "value" : "*"
        }
      ]
    }
  ]
}