Examine source code of Delete Download

{
  "description": "Shows the last downloaded item, and lets you open or delete it",
  "manifest_version": 2,
  "name": "Delete Last Download",
  "version": "1.0",
  "homepage_url": "https://github.com/nabendu82/Addons",
  "icons": {
    "32": "icons/logo_32.png",
    "64": "icons/logo_64.png",
    "128": "icons/logo_128.png"
  },
  "permissions": [
    "downloads",
    "downloads.open"
  ],
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/logo_64.png",
    "default_title": "Delete Last Download",
    "default_popup": "popup/download.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{047d423c-47a2-4556-808b-0fe7eebc9c96}"
    }
  }
}