Examine source code of File Downloader

{
  "name": "File Downloader",
  "commands": {
    "_execute_page_action": {
      "suggested_key": {
        "default": "Alt+Shift+D",
        "windows": "Alt+Shift+D",
        "mac": "Alt+Shift+D"
      }
    }
  },
  "short_name": "Multifile DL",
  "icons": {
    "16": "images/icon_16.png",
    "48": "images/icon_48.png",
    "128": "images/icon_128.png"
  },
  "description": "Quickly get the downloads and nothing else.",
  "version": "1.5",
  "permissions": [
    "<all_urls>",
    "downloads",
    "storage"
  ],
  "manifest_version": 2,
  "page_action": {
    "default_icon": {
      "19": "images/icon_19.png",
      "38": "images/icon_38.png"
    },
    "default_title": "File Downloader",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_idle",
      "all_frames": false
    }
  ],
  "options_ui": {
    "page": "options.html",
    "open_in_tab": false
  },
  "web_accessible_resources": [],
  "browser_specific_settings": {
    "gecko": {
      "id": "multiple@example.com"
    }
  }
}