Examine source code of Scrollbar Beats

{
  "manifest_version": 2,
  "name": "Scrollbar Beats",
  "version": "1.0",
  "description": "Plays pitched notes when the user scrolls up/down — higher pitch when scrolling up, lower when scrolling down.",
  "icons": {},
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "scrollbar-beats.js"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{cea53990-8062-4442-a9d9-a5d3c87e36b8}"
    }
  }
}