Examine source code of SaveAsUrl

{
  "name": "SaveAsUrl",
  "author": "Andre",
  "description": "Save the current URL in file \".url.download\" and take screenshot of visible Tab. To execute the save dialog press hotkey \"accel-shift-f12\".",
  "manifest_version": 2,
  "version": "0.0.5",
  "icons": {
    "32": "images/32x32.png",
    "48": "images/48x48.png",
    "64": "images/64x64.png",
    "144": "images/144x144.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "downloads",
    "tabs",
    "<all_urls>"
  ],
  "commands": {
    "main-action": {
      "suggested_key": {
        "default": "Ctrl+Shift+F12"
      },
      "description": "Send a event to the extension"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "@saveasurl"
    }
  }
}