Examine source code of KANTAN Chord

{
  "manifest_version": 3,
  "name": "__MSG_appName__",
  "version": "2025.3.6.0",
  "description": "__MSG_appDescription__",
  "default_locale": "en",
  "icons": {
    "16": "icons/IC-016.png",
    "48": "icons/IC-048.png",
    "128": "icons/IC-128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.ufret.jp/*",
        "*://gakufu.gakki.me/*",
        "*://www.gakufu.gakki.me/*",
        "*://music.j-total.net/*",
        "*://tabs.ultimate-guitar.com/*",
        "*://*.guitarians.com/*",
        "*://guitarians.com/*",
        "*://www.91pu.com.tw/*"
      ],
      "js": [
        "content_scripts.js"
      ],
      "run_at": "document_end"
    }
  ],
  "action": {
    "default_icon": {
      "16": "icons/IC-016.png"
    },
    "default_title": "__MSG_appName__",
    "default_popup": "popup.html"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{940de8b5-be39-45c6-931d-92653a8c2f8d}"
    }
  }
}