Examine source code of Token Counter for ChatGPT

{
  "manifest_version": 2,
  "name": "Token Counter for ChatGPT",
  "version": "2.7.1",
  "description": "Show the number of tokens in the current prompt for ChatGPT",
  "permissions": [
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://chat.openai.com/*"
      ],
      "js": [
        "contentScript.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{ca736991-ed93-418d-ac62-85777ed2ba8e}"
    }
  }
}