Examine source code of xkcd x2

{
  "manifest_version": 3,
  "name": "xkcd x2",
  "version": "1.1",
  "description": "Adds a link to the double-size image version to xkcd pages.",
  "browser_specific_settings": {
    "gecko": {
      "id": "{cd9afd04-a7d3-46b6-a8bd-714165d837a8}",
      "strict_min_version": "58.0"
    }
  },
  "icons": {
    "48": "icons/xkcd_x2_48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.xkcd.com/*"
      ],
      "js": [
        "x2Button.js"
      ]
    }
  ]
}