Examine source code of Haxle

{
  "name": "Haxle",
  "description": "Win at Hexle every day!",
  "version": "1.0",
  "manifest_version": 2,
  "action": {
    "default_icon": {
      "16": "/images/haxle16.png",
      "32": "/images/haxle32.png",
      "48": "/images/haxle48.png",
      "128": "/images/haxle128.png"
    },
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "/images/haxle16.png",
    "32": "/images/haxle32.png",
    "48": "/images/haxle48.png",
    "128": "/images/haxle128.png"
  }
}