Examine source code of Letterboxd Languages

{
  "manifest_version": 2,
  "name": "Language_Filter",
  "version": "1.0",
  "description": "Adds a filter option that displays languages./",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://letterboxd.com/*/list/*"
      ],
      "js": [
        "filter.js"
      ]
    }
  ],
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "*://api.themoviedb.org/*",
    "https://language-iso-code-api.herokuapp.com/*",
    "webNavigation",
    "tabs"
  ]
}