Examine source code of MangaReq

{
  "manifest_version": 2,
  "name": "MangaReq",
  "version": "1.0",
  "description": "adds a button to send a request to download the manga",
  "icons": {
    "48": "icon.svg"
  },
  "permissions": [
    "webRequest",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "mangaReq.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://mangadex.org/*",
        "https://manganato.com/manga*",
        "https://chapmanganato.com/manga*",
        "https://myanimelist.net/anime/*"
      ],
      "js": [
        "mangaReq.js"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{167228f3-be32-4d3a-8ef3-aff4f44ad94e}"
    }
  }
}