Examine source code of Instant Top Scroll

{
  "manifest_version": 2,
  "name": "Scroll to Top Button",
  "version": "1.0",
  "description": "Quickly scroll any page back to the top with one click.",
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Scroll to Top"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "scroll-to-top-button@example.com"
    }
  }
}