Examine source code of Abfahrt

{
  "name": "Abfahrt Extension",
  "description": "Abfahrt!",
  "version": "1.0",
  "manifest_version": 2,
  "permissions": [
    "activeTab",
    "scripting"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://*/*",
        "http://*/*"
      ],
      "run_at": "document_end",
      "js": [
        "background.js"
      ]
    }
  ],
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d673da67-f4a6-40ae-ab73-dffa8c2b5c1a}"
    }
  }
}