Examine source code of Notification Jingles

{
  "manifest_version": 2,
  "name": "Notification Jingles",
  "version": "1.0",
  "description": "Plays a short 2-3 note jingle when pages create a Notification or when a tab finishes loading, replacing the default ding.",
  "icons": {},
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{066b673a-edd3-43f2-8229-27a5befefca7}"
    }
  }
}