Examine source code of Page Word Count

{
  "manifest_version": 2,
  "name": "Page Word Count",
  "version": "1.0",
  "description": "Displays the word count of the current web page.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b0b82933-5c1c-4c4a-9597-28d3bf6e16b6}"
    }
  }
}