Examine source code of WordCounter pro

{
  "manifest_version": 3,
  "name": "WordCounter",
  "version": "1.0.0",
  "description": "Count words and characters in selected text",
  "permissions": [
    "storage",
    "activeTab"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_title": "WordCounter"
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "author": "XMP <lanhanh64529@gmail.com>",
  "homepage_url": "https://github.com/xmp-tools/wordcounter",
  "browser_specific_settings": {
    "gecko": {
      "id": "wordcounter@xmpi.net"
    }
  }
}