Examine source code of Site Volume Controller

{
  "manifest_version": 2,
  "name": "Site Volume Controller",
  "version": "2.2",
  "description": "Control and remember audio/video volume per site, with gain boost and popup UI.",
  "permissions": [
    "activeTab",
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{aa53f413-dc0d-4636-af52-1af5642000d6}"
    }
  }
}