Examine source code of Fast scroll

{
  "manifest_version": 2,
  "name": "Fast scroll",
  "version": "1.4",
  "description": "Hold left alt key to increase scroll speed of element, useful for viewing text heavy sites.",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "fast-scroll.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{816d07c7-0366-4ecc-b72d-db01aa8ea5a9}"
    }
  }
}