Adds support for opening magnet:// links in Deluge Web. If you want this to work for you, you'll likely have to configure the @match url to be the url of your Deluge Web, and set `dom.registerProtocolHandler.insecure.enabled` to true in your Firefox about:config, as by default protocol handlers cannot be registered on http sites.

deluge-magnet-protocol-handler.js

// ==UserScript==
// @name Deluge Protocol Handler
// @namespace Violentmonkey Scripts
// @match http://192.168.86.74:8112/*
// @grant none
// ==/UserScript==

if (navigator.registerProtocolHandler)
  navigator.registerProtocolHandler("magnet", "http://192.168.86.74:8112/?magnet=%s", "Deluge");

const waitUntil = (condition, action) => {
  if (condition()) {
    action()
    return;
  }
  
  setTimeout(() => waitUntil(condition, action), 500);
}

const addTorrent = (path) => {
  deluge.client.web.add_torrents([{
      path: path,
      options: {
          file_priorities: [],
          add_paused: false,
          compact_allocation: false,
          download_location: "/media/Seagate/Downloads",
          move_completed: true,
          move_completed_path: "/media/Seagate/AudioBooks",
          max_connections: 0,
          max_download_speed: -1,
          max_upload_slots: -1,
          max_upload_speed: -1,
          prioritize_first_last_pieces: true
    }
  }]);
}

const canAddTorrent = () => deluge && deluge.client && deluge.client.web && deluge.client.web.add_torrents;

window.addEventListener('load', () => {
  const searchParams = new URLSearchParams(window.location.search);
  if (!searchParams.has('magnet'))
    return;
  
  const magnetLink = searchParams.get('magnet');
  waitUntil(canAddTorrent, () => addTorrent(magnetLink));
  
});