Examine source code of Volume Control Slider

{
  "manifest_version": 2,
  "name": "Volume Control",
  "version": "1.3",
  "description": "Control the volume of web pages.",
  "permissions": [
    "tabs",
    "activeTab",
    "storage",
    "<all_urls>"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a01d8df0-db4d-4fe2-b7b0-cb61ca38e55d}"
    }
  }
}