firebase.json

{
    "hosting": {
      "public": "build",
      "cleanUrls": true,
      "headers": [
        {
          "source": "**/*",
          "headers": [
            {
              "key": "Access-Control-Allow-Origin",
              "value": "*"
            }
          ]
        },
        {
          "source" : "**/*.@(jpg|jpeg|gif|png|svg)",
          "headers" : [
            {
              "key" : "Cache-Control",
              "value" : "max-age=2592000"
            }
          ]
        },
        {
          "source" : "**/*.@(eot|otf|ttf|ttc|woff|font.css)",
          "headers" : [
            {
              "key" : "Cache-Control",
              "value" : "max-age=2592000"
            }
          ]
        }
      ],
      "ignore": [
        "firebase.json",
        "package.json",
        "README.md",
        "node_modules/**",
        "src/**",
        ".git/**"
      ]
    }
  }