Examine source code of Link Preview

{
  "manifest_version": 3,
  "name": "Link Preview",
  "version": "1.0",
  "description": "Get previews of links, when you hover over them.",
  "action": {
    "default_popup": "popup/index.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "links-previews@jdm.dev"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "main.js"
      ]
    }
  ]
}