Examine source code of Volume Control Master

{
  "manifest_version": 2,
  "name": "Volume Master",
  "version": "1.0.0",
  "description": "Control and boost volume for audio and video elements on web pages (Manifest V2).",
  "icons": {},
  "permissions": [
    "activeTab",
    "tabs",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_title": "Volume Master",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content-script.js"
      ],
      "run_at": "document_end"
    }
  ],
  "applications": {
    "gecko": {
      "id": "volume-master@example.com"
    }
  }
}