Are you fed up with trolls on FB? This script adds a "Find trolls" button right next to the "Home" link in the blue bar. Update the trolls list to include all trolls you know. Push the "Find trolls" to mark the comments from these users with a troll face.

fb_find_trolls.js

// ==UserScript==
// @name          Facebook troll finder
// @namespace     tag:[email protected],2018:andrask
// @description   Find trolls in FB comment authors
// @include       http://www.facebook.com/*
// @include       https://www.facebook.com/*
// @grant         GM_setValue
// @grant         GM_getValue
// ==/UserScript==

// License: MIT
// Usage: load it in tampermonkey
// Disclaimer: I'm not a JS developer just really hate trolls and want to mark them.

var trolls = new Set([
    "fbname1",
    "fbname2",
]);

function findTrolls() {
    var trollVersion = 1;
    console.log("Finding trolls");
    var  profiles = document.querySelectorAll('a.UFICommentActorName');
    var i;
    for (i = 0; i < profiles.length; i++) {
        console.log("Finding trolls");
        var profile = profiles[i];
        if (profile.getAttribute('trollVer') == trollVersion) continue;
        var profileUrl = new URL(profile);
        var id = profileUrl.searchParams.get('id');
        if (!id) {
            id = profileUrl.pathname.substring(1);
        }
        console.log(id);
        if (trolls.has(id)) {
            profile.insertAdjacentHTML("afterend", "&nbsp;<img width='16px' height='16px' src='https://files.gamebanana.com/img/ico/sprays/spray_trollface_copy.png'></img>");
            profile.style = "text-decoration: underline line-through overline;";
        }
        profile.setAttribute('trollVer', trollVersion);
    }
    return;
}
window.onload = function() {
  var findTrollButton = '<div class="_4kny _2s24"><div class="_3qcu _cy7" data-click="home_icon" id="u_0_n"><a id="_dsfjshfeuudsh" data-gt="{&quot;chrome_nav_item&quot;:&quot;home_chrome&quot;}" href="#" class="_2s25" accesskey="9">Find trolls</a></div></div>';
  var homeLink = document.querySelectorAll('div._4kny')[3];
  homeLink.insertAdjacentHTML("afterend", findTrollButton);
  document.getElementById("_dsfjshfeuudsh").addEventListener('click', findTrolls, false);
};