Examine source code of Volume Master

{
  "manifest_version": 2,
  "name": "Volume Master",
  "version": "1.0",
  "description": "Volume Master allows you to easily control the volume of your browser tabs, giving you precise audio management for a better listening experience",
  "content_scripts": [
    {
      "matches": [
        "*://*.9gag.com/*"
      ],
      "js": [
        "jquery/jquery-min.js",
        "index.js"
      ],
      "css": [
        "css/styles.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{f5a86890-35f9-4134-bb29-445c7e4ef1a8}"
    }
  }
}