Examine source code of Tab Mute Manager

{
  "manifest_version": 2,
  "name": "Tab Mute Manager",
  "version": "1.0",
  "description": "Mute or unmute all tabs at once",
  "browser_specific_settings": {
    "gecko": {
      "id": "{f65e04f7-2748-4ebf-b603-4ed3828fe8ad}",
      "strict_min_version": "112.0"
    }
  },
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_title": "Tab Mute Manager",
    "default_popup": "popup.html"
  }
}