Examine source code of Word Counters

{
  "manifest_version": 2,
  "name": "Word Counter",
  "version": "1.0",
  "description": "Count the number of words on the current page.",
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6aed0c35-baa9-469d-8717-98ccf70bb701}"
    }
  }
}