Examine source code of Link Preview

{
  "manifest_version": 2,
  "name": "Link Preview",
  "version": "1.0",
  "description": "Show preview of linked page on hover",
  "permissions": [
    "activeTab",
    "tabs",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{c6cd8a4b-0edc-4113-b79e-c3033a0e7e0d}",
      "strict_min_version": "116.0"
    }
  },
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ]
}