Examine source code of Shortshare

{
  "name": "Shortshare",
  "description": "Shortshare Extension for Mozilla Firefox. Get Shortshare for your Mac on http://shortshare.app.",
  "version": "1.0.1",
  "manifest_version": 2,
  "permissions": [
    "http://localhost:60101/*",
    "activeTab",
    "webRequest"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "/images/shortshare16.png",
      "48": "/images/shortshare48.png",
      "128": "/images/shortshare128.png"
    }
  },
  "icons": {
    "16": "/images/shortshare16.png",
    "48": "/images/shortshare48.png",
    "128": "/images/shortshare128.png"
  }
}