Examine source code of IP Lookup

{
  "manifest_version": 2,
  "name": "IP Lookup",
  "short_name": "Search the geolocation of IP addresses",
  "description": "It uses a database of IP addresses, provided from extreme-ip-lookup.com, that are associated to cities and to other informations",
  "version": "1.6.2resigned1",
  "minimum_chrome_version": "38",
  "applications": {
    "gecko": {
      "id": "@ip_lookup",
      "strict_min_version": "45.0"
    }
  },
  "permissions": [
    "tabs",
    "<all_urls>"
  ],
  "icons": {
    "16": "assets/icon_16.png",
    "128": "assets/icon_128.png"
  },
  "browser_action": {
    "default_icon": {
      "19": "assets/icon_16.png",
      "38": "assets/icon_128.png"
    },
    "default_popup": "data/index.html"
  }
}