Examine source code of Upload Preview

{
  "manifest_version": 3,
  "name": "Upload Preview",
  "version": "1.1.0",
  "description": "Quick-pick an image from your clipboard or recent downloads when a site asks you to upload a file.",
  "browser_specific_settings": {
    "gecko": {
      "id": "upload-preview-addon@gmail.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "downloads",
    "clipboardRead",
    "storage"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content-script.js"
      ],
      "all_frames": true,
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "overlay.css"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  }
}