Examine source code of event pagee

{
  "name": "Context Menus Sample (with Event Page)",
  "description": "Shows some of the features of the Context Menus API using an event page",
  "version": "0.7",
  "permissions": [
    "contextMenus"
  ],
  "background": {
    "persistent": false,
    "scripts": [
      "sample.js"
    ]
  },
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "{d5bcafad-17c9-4aca-83d3-107304c16745}"
    }
  }
}