Examine source code of Favicon Battle

{
  "manifest_version": 2,
  "name": "Favicon Battle",
  "version": "1.0.0",
  "description": "Use tab favicons as battle pieces — drag them into the arena and watch them fight!",
  "permissions": [
    "tabs",
    "storage",
    "<all_urls>"
  ],
  "browser_action": {
    "default_title": "Favicon Battle",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "favicon-battle@example.com",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "collects": false
      }
    }
  },
  "icons": {
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  }
}