Examine source code of Link Highlight

{
  "manifest_version": 2,
  "name": "Link Highlight",
  "description": "Highlight external links in one color and internal links in another for instant domain awareness",
  "version": "1.2",
  "icons": {
    "64": "ico/64.png",
    "128": "ico/128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{0b4ec2b1-f9a8-45fd-bab8-500ae3297871}",
      "strict_min_version": "90.0"
    }
  }
}