Examine source code of Page Word Counter

{
  "manifest_version": 2,
  "name": "Page Word Counter",
  "version": "1.0",
  "description": "Counts the words on the current page.",
  "permissions": [
    "activeTab",
    "tabs",
    "<all_urls>"
  ],
  "browser_action": {
    "default_title": "Count Words",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d32f3281-565b-4362-9057-942ff4fc3dfe}"
    }
  }
}