Examine source code of Quick Screenshot it

{
  "manifest_version": 2,
  "name": "Quick Screenshot",
  "version": "1.0",
  "description": "Capture the visible area of the current tab as a PNG and download it.",
  "permissions": [
    "activeTab",
    "tabs",
    "downloads"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Quick Screenshot"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6ac70c95-cf52-41ee-8835-3f2165116284}"
    }
  }
}