Adds table filtering to the sidekiq busy jobs list and toggles the visibility of the processes table. To install click the `Raw` button and your userscript extension will take it from there.

sidekiq_busy_jobs_enhancement.user.js

// ==UserScript==
// @name         Sidekiq BusyJob Helper
// @namespace    http://bigethan.com/
// @version      0.1
// @description  On Sidekiq's UI fro busy jobs: Toggles the workers table and adds a way to filter the busy jobs table
// @author       bigethan
// @match        https://*/sidekiq/busy
// @grant        none
// ==/UserScript==

(function (document) {
  "use strict";
  let searchInput = document.createElement("input");
  searchInput.setAttribute("type", "text");
  searchInput.setAttribute("id", "job_search");
  searchInput.setAttribute("placeholder", "Filter Listing");
  searchInput.addEventListener("input", filterTable);
  searchInput.style.verticalAlign = "text-bottom";
  searchInput.style.marginLeft = "1em";
  let jobsXpath = "//h3[contains(text(),'Jobs')]";
  let jobsElement = document.evaluate(
    jobsXpath,
    document,
    null,
    XPathResult.FIRST_ORDERED_NODE_TYPE,
    null
  ).singleNodeValue;
  jobsElement.parentElement.appendChild(searchInput);
  jobsElement.style.display = "inline-block";

  function filterTable() {
    const filter = document.querySelector("#job_search").value.toUpperCase();
    const trs = document.querySelectorAll(".table_container .workers tbody tr");
    trs.forEach(
      (tr) =>
        (tr.style.display = [...tr.children].find((td) =>
          td.innerHTML.toUpperCase().includes(filter)
        )
          ? ""
          : "none")
    );
  }

  let processXpath = "//h3[contains(text(),'Processes')]";
  let processesElement = document.evaluate(
    processXpath,
    document,
    null,
    XPathResult.FIRST_ORDERED_NODE_TYPE,
    null
  ).singleNodeValue;
  let small = document.createElement("small");
  let text = document.createTextNode(" (Click to show/hide)");
  small.appendChild(text);
  processesElement.appendChild(small);
  processesElement.addEventListener("click", toggleTable);
  toggleTable();

  function toggleTable() {
    const tbody = document.querySelector(".table_container .processes tbody");
    if (tbody.offsetParent === null) {
      tbody.style.display = "table-row-group";
    } else {
      tbody.style.display = "none";
    }
  }
})(document);