Get_Wiki_format.user.js

// ==UserScript==
// @name        Get Wiki format
// @namespace   bugzilla
// @include     https://bugzilla.mozilla.org/show_bug.cgi?id=*
// @version     1
// @grant       GM_setClipboard
// ==/UserScript==
var title = document.getElementById("mode-container");
var button = document.createElement("button");
button.type = "button";
button.innerHTML = "Copy for Wiki"
button.className = "major";
title.insertBefore(button, title.firstChild);

button.onclick = function(e) {
  var bugid = document.getElementById("this-bug").innerText;
  var bugdesc = document.getElementById("field-value-short_desc").innerText;
  bugid = bugid.replace(/\s/g, '|')
  var res  = "* {{" + bugid + "}} - " + bugdesc;
  // console.log(res)
  GM_setClipboard (res);
}