Examine source code of DECK

{
  "manifest_version": 2,
  "version": "1.0.1",
  "name": "DECK",
  "description": "A extension which saves images which user downloads!",
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ]
    }
  ],
  "permissions": [
    "downloads",
    "tabs",
    "storage",
    "*://domain/*"
  ],
  "browser_action": {
    "default_title": "Download Images from FreePik",
    "default_popup": "templates/popup.html"
  },
  "background": {
    "scripts": [
      "background.js",
      "imageDownload.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d5ad2162-f5fc-4844-bb80-7acfd3570003}"
    }
  }
}