proxy-random.user.js

// ==UserScript==
// @name         Proxy Random
// @namespace    http://stackoverflow.com/users/982924/rasg
// @author       RASG
// @icon         https://www.clipartmax.com/png/full/114-1147589_reverse-proxy-reverse-proxy-icon.png
// @version      2012.06.14.1010
// @description  Load webpages and links through a random proxy.
// @include      http*://*
// ==/UserScript==

var matriz = ['https://cache-001.appspot.com/', 'https://cache-003.appspot.com/', 'https://cache-017.appspot.com/', 'https://meme-darwin.appspot.com/'];
var proxy = matriz[Math.floor(Math.random() * matriz.length)];
var temproxy = 0;
var url = window.location.href;

for (i in matriz) {
  if (url.indexOf(matriz[i]) > -1) {
    temproxy = 1;
  }
}

if (temproxy == 0) {
  window.location.replace(location.href.replace(location.protocol + '//', proxy));
  for (var i = 0, link; (link = document.links[i]); i++) {
    if (link.href.indexOf(proxy) < 0) {
      link.href = link.href.replace(link.href.substring(0, 7), proxy);
    }
  }
}