Examine source code of Scroll Tempo

{
  "manifest_version": 2,
  "name": "Scroll Tempo",
  "version": "1.0",
  "description": "Adjusts a background rhythmic soundtrack based on your scroll speed: faster scroll → faster tempo.",
  "icons": {
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "tabs",
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_icon": "icons/icon-48.png",
    "default_title": "Scroll Tempo",
    "default_popup": "popup.html"
  },
  "applications": {
    "gecko": {
      "id": "scrolltempo@example.com"
    }
  }
}