Examine source code of IIIF Downloadingna

{
  "manifest_version": 2,
  "name": "IIIF Download",
  "version": "0.2",
  "description": "Allows user to download fullsize content from digital libraries serving content using IIIF technology.",
  "icons": {
    "48": "icon48.png",
    "96": "icon96.png"
  },
  "permissions": [
    "activeTab",
    "tabs",
    "downloads",
    "*://gallica.bnf.fr/*",
    "*://nutrisco-patrimoine.lehavre.fr/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://gallica.bnf.fr/*",
        "*://nutrisco-patrimoine.lehavre.fr/*"
      ],
      "js": [
        "iiif_download_gallica.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "icon_inactive.png",
    "default_title": "No highdef found on this page",
    "browser_style": true
  },
  "web_accessible_resources": [
    "icon_active.png",
    "icon_inactive.png"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      },
      "id": "{6c406799-cdbd-4cac-af7b-b38bd8647e6f}"
    }
  }
}