Examine source code of sync_cookies

{
  "manifest_version": 2,
  "name": "sync_cookies",
  "description": "manifest.json description",
  "version": "1.2.2",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "96": "icon/96.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "activeTab",
    "cookies",
    "storage",
    "*://*/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "async_cookies",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d1c1cda2-7c2c-4f52-957b-67ead03b67ae}"
    }
  }
}