It will set a max width of wikipedia for better readibility.
// ==UserScript==
// @name MaxWidth for WikiPedia
// @author h.zhuang
// @version 2014.11.18
// @description It will set a max width of wikipedia for better readibility.
// @lastchanges Initial release
// @namespace wikipedia.org
// @grant GM_addStyle
// @include http://wikipedia.org/*
// @include https://wikipedia.org/*
// @include http://*.wikipedia.org/*
// @include https://*.wikipedia.org/*
// ==/UserScript==
GM_addStyle("#mw-head-base {display:none;}\
#content,#bodyContent {max-width:760px !important;}\
#mw-content-text {max-width:680px !important;}\
.mw-body {max-width:999px !important;}");