Examine source code of robots.txt viewer

{
  "manifest_version": 2,
  "author": "Nico Hemkes",
  "name": "robots.txt viewer",
  "short_name": "robots.txt",
  "description": "look into a robots.txt file on websites with a single click.",
  "homepage_url": "https://www.robots-viewer.com/",
  "version": "1.6.1",
  "browser_action": {
    "browser_style": true,
    "default_title": "robots.txt viewer",
    "default_icon": "img/icon_128.png",
    "default_popup": "popup.html"
  },
  "icons": {
    "48": "img/icon.png"
  },
  "permissions": [
    "activeTab",
    "https://www.robots-viewer.com/"
  ],
  "developer": {
    "name": "turbopixel",
    "url": "https://hemk.es/"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b82039dd-1ded-4a66-b8b0-db0ec30abe45}"
    }
  }
}