Examine source code of Volume Control

{
  "manifest_version": 2,
  "name": "Volume Control",
  "version": "1.0",
  "description": "Control the volume of audio on the current page.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{816aeaa4-ab6c-43f1-93c9-72a9ac39fe23}"
    }
  }
}