Examine source code of Selection Word Counter

{
  "manifest_version": 2,
  "name": "Selection Word Counter",
  "version": "1.0.0",
  "description": "Counts words and characters in selected page text.",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "activeTab",
    "notifications"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "selection-word-counter-425a7b51@localtools.example",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "browser_action": {
    "default_title": "Selection Word Counter",
    "default_icon": {
      "48": "icons/icon-48.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}