Examine source code of Sign Tester

{
  "name": "Sign Tester",
  "description": "Simple extension to play around with minecraft signs",
  "version": "1.2.6",
  "manifest_version": 2,
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://crowdin.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "/images/icon48.png",
      "128": "/images/icon128.png"
    }
  },
  "icons": {
    "48": "/images/icon48.png",
    "128": "/images/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c8193582-6bec-49ee-826d-3c001b1ba300}"
    }
  }
}