Examine source code of Ad Counter

{
  "manifest_version": 2,
  "name": "Ad Counter",
  "version": "1.0",
  "description": "Counts the number of ad elements on the current page.",
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_title": "Count Ads",
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a7f24f99-e080-4119-862e-d26cbcd273d1}"
    }
  }
}