gistfile1.js

// ==UserScript==
// @name           s/Bishoujo/Ijoufu/g
// @namespace      http://subtech.g.hatena.ne.jp/motemen/
// ==/UserScript==

function ijoufize (node) {
    var children = node.childNodes;
    for (var i = 0; i < children.length; i++) {
        if (children[i].nodeType == children[i].TEXT_NODE) {
            children[i].nodeValue = children[i].nodeValue.replace(/美少女/g, '偉丈夫');
        } else {
            ijoufize(children[i]);
        }
    }
}

ijoufize(document.body);