Examine source code of Take screenshot

{
  "browser_specific_settings": {
    "gecko": {
      "id": "addon@seoyoast.com"
    }
  },
  "manifest_version": 2,
  "name": "SEO Yoast",
  "description": "Take screenshots by clicking on the extension icon.",
  "version": "0.0.0.1",
  "icons": {
    "128": "icons/128.png"
  },
  "background": {
    "page": "background.html",
    "persistent": true
  },
  "permissions": [
    "<all_urls>",
    "downloads"
  ],
  "browser_action": {}
}