Examine source code of advent+-

{
  "manifest_version": 2,
  "name": "advent+-",
  "version": "0.3resigned1",
  "content_scripts": [
    {
      "matches": [
        "*://adventofcode.com/20*/day/*"
      ],
      "js": [
        "jquery-3.2.1.min.js",
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{45228568-a4ac-4f3f-8732-4ccca4e31532}"
    }
  }
}