Eu mesmo descobri e criei um script do Tampermonkey para fazer isso. Código-fonte aqui , assim como abaixo:
// ==UserScript==
// @name Remove Messenger Tracker
// @namespace http://tampermonkey.net/
// @version 1.2
// @homepage https://github.com/Puffycheeses/TamperMonkeyMessengerCleaner/
// @updateURL https://github.com/Puffycheeses/TamperMonkeyMessengerCleaner/raw/master/Remove%20Messenger%20Tracker.user.js
// @description Removes annoying Facebook Tracker
// @author Puffycheeses
// @match *://www.messenger.com/*
// @grant none
// @require http://code.jquery.com/jquery-1.12.4.min.js
// ==/UserScript==
var i=0;
//var cleaned = 0; //For logging can ignore
var links = document.getElementsByTagName('a');
setInterval(function(){
var links = document.getElementsByTagName('a');
//console.log('Scanning for new links'); //Log that its actually working
}, 2500);
setInterval(function(){
link = links[i];
if(i < links.length) {
if(link.href.includes('https://l.messenger.com/l.php?u=')){
var rep = link.href;
var ret = rep.replace("https://l.messenger.com/l.php?u=", "").replace(/%3A/g, ":").replace(/%2F/g, "/").replace(/%3F/g, "?").replace(/%3D/g, "=");
var rek = ret.substring(0, ret.indexOf('&h='));
//console.log(rek); //For displaying the found links
link.href = rek;
//cleaned += 1; //For displaying how many links were found
}
}
if(i < links.length) {
i+=1;
} else {
//if(cleaned > 0){ //This who section was to display how many links have been cleaned
// console.log(cleaned + ' Links found and cleaned');
//}
//cleaned = 0;
i=0;
}
}, 100);