Examine source code of SilentStart

{
  "manifest_version": 2,
  "name": "SilentStart",
  "version": "1.0",
  "description": "Automatically set tab/media volume when playback starts. Per-domain rules, temp unmute hotkey, preserves previous state where possible.",
  "icons": {
    "48": "icon-48.png",
    "128": "icon-128.png"
  },
  "permissions": [
    "storage",
    "tabs",
    "<all_urls>",
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "web_accessible_resources": [
    "silentstart.html",
    "silentstart.js",
    "silentstart.css"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e1311fbb-9d89-46be-b793-f7129c293a9d}"
    }
  }
}