Examine source code of SponSpin

{
  "manifest_version": 2,
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "name": "SponSpin",
  "version": "1.9",
  "description": "Geniessen Sie gewisse Seiten auf SPON mit extra-scharfem Senf!",
  "homepage_url": "http://spin.sponspin.org",
  "icons": {
    "16": "icons/sponspin-16.png",
    "48": "icons/sponspin-48.png",
    "128": "icons/sponspin-128.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "notifications",
    "http://*.spiegel.de/*",
    "https://*.spiegel.de/*",
    "http://*.bento.de/*",
    "https://*.bento.de/*",
    "https://i88i.org/*"
  ],
  "browser_action": {
    "default_icon": "icons/sponspin-48.png",
    "default_title": "Geben Sie Ihren Senf dazu!",
    "default_popup": "showURL.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.spiegel.de/*",
        "*://*.bento.de/*"
      ],
      "js": [
        "jquery.js",
        "showURL.js"
      ]
    }
  ]
}