Examine source code of MP3Cow

{
  "manifest_version": 2,
  "name": "MP3Cow",
  "version": "1.0",
  "description": "Convert YouTube Videos to mp3 files with MP3Cow",
  "homepage_url": "https://mp3cow.com",
  "icons": {
    "48": "icons/48.png",
    "96": "icons/96.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icons/32.png",
    "default_title": "MP3Cow",
    "default_popup": "popup/popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c5e4a9d2-1f3a-4d2e-a7b3-9c8d1e2f3a4b}"
    }
  }
}