Transforms @mention@twitter.com to a bona fide link to Twitter in the Mastodon web interface.

twitter-mentions-linker-for-mastodon.user.js

// ==UserScript==
// @name Twitter mentions linker for Mastodon
// @description Transforms @mention@twitter.com to a bona fide link to Twitter in the Mastodon web interface.
// @include https://boitam.eu/*
// ==/UserScript==

var observer = new MutationObserver(function(mutations) {
      mutations.forEach(function(mutation) {
        var nodes = Array.prototype.slice.call(mutation.addedNodes);
        nodes.forEach(function(node) {
          if (node.parentElement.classList.contains("detailed-status__wrapper") || node.parentElement.classList.contains("item-list")) {
            node.parentElement.querySelectorAll(".status__content").forEach(function(e){ e.innerHTML = e.innerHTML.replace(/(@(\w{1,50})@twitter\.com)\b/gi, function(m, a, b){ return "<a href='https://twitter.com/" + b + "'>" + a + "</a>" })})

          }
        });
      });
    });

    observer.observe(document.querySelector(".app-body"), {
      childList: true,
      subtree: true,
    });