Examine source code of Count Text Stats

{
  "manifest_version": 2,
  "name": "Count Text Stats",
  "version": "1.0.0",
  "description": "Count words and characters for the selection or the whole page (Supports English Language).",
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{697a7c80-2cc1-4da7-8a94-20f268aa7470}",
      "strict_min_version": "127.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_title": "Count Text Stats",
    "default_popup": "popup.html",
    "default_icon": {
      "64": "icon64.png",
      "128": "icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ]
}