Examine source code of Drag and Save

{
  "manifest_version": 2,
  "name": "Drag to Save",
  "version": "1.0",
  "description": "Сохраняйте изображения, просто перетаскивая их.",
  "permissions": [
    "downloads"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "icons": {
    "16": "Icons/icon-16.png",
    "32": "Icons/icon-32.png",
    "48": "Icons/icon-48.png",
    "128": "Icons/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4f0353dd-6de9-42bd-be41-8dc1205a3087}"
    }
  }
}