Examine source code of WASD Scrolling

{
  "manifest_version": 2,
  "name": "WASD Scroller",
  "version": "1.0",
  "description": "Scroll pages using W, A, S, D keys.",
  "permissions": [
    "<all_urls>"
  ],
  "icons": {
    "48": "icons/wasd-48.png",
    "96": "icons/wasd-96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "app.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background_scripts/background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{9b547e46-7007-4e0c-895a-0488204535b8}"
    }
  }
}