Examine source code of Reading Info

{
  "manifest_version": 3,
  "version": "1.1",
  "name": "Reading Info",
  "description": "Show reading time, word, and character counts in a toolbar popup.",
  "browser_specific_settings": {
    "gecko": {
      "id": "readingInfo@cubeleco"
    }
  },
  "action": {
    "browser_style": true,
    "default_popup": "popup.html",
    "default_icon": {
      "250": "icon.png"
    }
  },
  "icons": {
    "250": "icon.png"
  },
  "commands": {
    "_execute_action": {
      "description": "Open toolbar popup"
    }
  },
  "permissions": [
    "activeTab",
    "scripting",
    "storage"
  ]
}