Examine source code of Sound Master

{
  "manifest_version": 2,
  "name": "Sound Master",
  "description": "Control and boost audio and video players in the current tab.",
  "version": "1.2.0",
  "permissions": [
    "tabs",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_title": "Sound Master",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png"
    }
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "sound-master-5d491992-767c-4a2e-9c4c-64a3bb302574@addons.mozilla.org",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}