Examine source code of TuneTransporter

{
  "manifest_version": 3,
  "name": "TuneTransporter",
  "version": "1.4.2",
  "description": "Automatically redirects music links between Spotify and YouTube Music, with copy tools.",
  "icons": {
    "16": "icons/icon16.jpeg",
    "32": "icons/icon32.jpeg",
    "48": "icons/icon48.jpeg",
    "128": "icons/icon128.jpeg"
  },
  "permissions": [
    "storage",
    "scripting",
    "tabs"
  ],
  "host_permissions": [
    "*://open.spotify.com/*",
    "*://music.youtube.com/*",
    "*://www.youtube.com/*"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_title": "TuneTransporter Settings"
  },
  "background": {
    "scripts": [
      "browser-polyfill.min.js",
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://open.spotify.com/track/*",
        "https://open.spotify.com/album/*",
        "https://open.spotify.com/artist/*"
      ],
      "js": [
        "browser-polyfill.min.js",
        "utils.js",
        "spotify2ytm-content.js"
      ],
      "run_at": "document_idle"
    },
    {
      "matches": [
        "https://music.youtube.com/watch*",
        "https://music.youtube.com/playlist?list=*",
        "https://music.youtube.com/channel/*"
      ],
      "js": [
        "browser-polyfill.min.js",
        "utils.js",
        "ytm2spotify-content.js"
      ],
      "run_at": "document_idle"
    },
    {
      "matches": [
        "*://www.youtube.com/watch*"
      ],
      "js": [
        "browser-polyfill.min.js",
        "yt-fallback-content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "some1sm@some1sm.com"
    }
  }
}