Examine source code of KaraokeQuiet

{
  "manifest_version": 2,
  "name": "KaraokeQuiet",
  "version": "1.0",
  "description": "Reduce instrumental/background volume automatically when lyrics appear on the page (rule-based detection).",
  "icons": {},
  "permissions": [
    "storage",
    "activeTab",
    "tabs"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "content.css"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_action": {
    "default_title": "KaraokeQuiet",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a9b6c27c-a6ee-4776-9a36-f4bd938ed13b}"
    }
  }
}