Examine source code of Custom Shortcut Toolbar

{
  "manifest_version": 2,
  "name": "Custom Shortcut Toolbar",
  "version": "1.0",
  "description": "Quick access toolbar for favorite sites.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5706c7a0-6393-44b5-a057-16c7c54cbad2}"
    }
  }
}