Chrome 19.0.1084.56、Safari 5.1.7(NinjaKit 0.9.1)、Opera 11.64でも動作するようにし、また、適用するCSSを変更した。

pixiv_staccfeed_illust_larger.user.js

// ==UserScript==
// @id             pixiv staccfeed illust larger
// @name           pixiv staccfeed illust larger
// @namespace      http://retlet.net/
// @author         retlet
// @contributer    saitamanodoruji
// @version        0.4.1
// @update         2012-06-14T10:07:54.763Z(GMT+09:00)
// @description    nya-n.
// @include        http://www.pixiv.net/stacc/*
// @run-at         document-end
// @priority       0
// @compatibility  Firefox 13.0(Scriptish 0.1.7), Chrome 19.0.1084.56, Safari 5.1.7(NinjaKit 0.9.1), Opera 11.64 on Windows 7 Home Premium SP1 64bit
// @charset        UTF-8
// ==/UserScript==

/*jslint browser: true, maxlen: 80*/
// Edition 2012-05-09

(function executeIllustLarger(doc) {
    'use strict';

    var timeline, modifyIllusts, staccPage;

    timeline = doc.getElementById('stacc_center_timeline');

    if (!timeline) {
        return;
    }

    doc.head.appendChild(doc.createElement('style')).textContent = [
        '.stacc_ref_thumb {',
        '  position: relative !important;',
        '}',
        '.stacc_ref_thumb .stacc_layout_row_top > ' +
            'div:first-child:not([class]) {',
        '  padding-top: 50px !important;',
        '}',
        '.stacc_ref_illust_side {',
        '  position: absolute !important;',
        '  left: 0 !important;',
        '}',
        '.stacc_ref_illust_img img {',
        '  max-width: 500px !important;',
        '}'
    ].join('\n');

    modifyIllusts = function modifyIllusts(evt) {
        var node, illusts, illustsLen, illust;

        node = evt.target;

        if (!(node.className && node.classList.contains('stacc_page'))) {
            return;
        }

        illusts = node.querySelectorAll(
            '.stacc_ref_illust_img img[src*="_s."]'
        );
        illustsLen = illusts.length;

        while (illustsLen) {
            illust = illusts[illustsLen -= 1];

            illust.src = illust.src.replace('_s.', '_m.');
        }
    };

    staccPage = timeline.querySelector('.stacc_page');

    if (staccPage) {
        modifyIllusts({target: staccPage});
    }

    timeline.addEventListener('DOMNodeInserted', modifyIllusts);
}(document));