Examine source code of Website Volume Controller

{
  "manifest_version": 2,
  "name": "Tab Volume Controller",
  "version": "1.0",
  "description": "Control volume individually for each website",
  "permissions": [
    "tabs",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/volume-48.png",
      "96": "icons/volume-96.png"
    }
  },
  "icons": {
    "48": "icons/volume-48.png",
    "96": "icons/volume-96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{f0716578-659e-4b6c-a319-1790251d4802}"
    }
  }
}