Examine source code of Dofollow Link Checker

{
  "manifest_version": 2,
  "name": "Dofollow Link Checker",
  "version": "1.0",
  "description": "Highlights dofollow links on web pages",
  "icons": {
    "48": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8845230a-079b-4093-a291-8e336f729103}"
    }
  }
}