Examine source code of Better Howrse

{
  "name": "__MSG_appName__",
  "description": "__MSG_appDesc__",
  "default_locale": "fr",
  "version": "2.1.1",
  "manifest_version": 2,
  "author": "TC-Dev",
  "icons": {
    "16": "/images/icon-16x16.png",
    "32": "/images/icon-32x32.png",
    "48": "/images/icon-48x48.png",
    "128": "/images/icon-128x128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.equideow.com/*",
        "*://*.howrse.com/*",
        "*://*.howrse.no/*"
      ],
      "run_at": "document_end",
      "js": [
        "translation.js",
        "loadingDisplayObserver.js",
        "moreInfos.js",
        "horseStats.js",
        "foodSelect.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{9f7cd518-a395-4c28-96e6-0a0e578efad1}"
    }
  }
}