View full image sizes on click

Question

Inspired by a meta question, here's a script that makes every image in a post also open itself at full size in a new window/tab when clicked.

It will ignore any images already manually linked.

Please suggest any improvements, or better yet submit a pull request on GitHub.

The current version can be found at and installed from here.

// ==UserScript==
// @name          SEImageExpander
// @namespace     http://vulpin.com/
// @description   Let people click on images to view the full size
// @match         *://*.askubuntu.com/*
// @match         *://*.mathoverflow.net/*
// @match         *://*.onstartups.com/*
// @match         *://*.serverfault.com/*
// @match         *://*.stackapps.com/*
// @match         *://*.stackexchange.com/*
// @match         *://*.stackoverflow.com/*
// @match         *://*.superuser.com/*
// @version       1.0.4
// @grant         none
// ==/UserScript==

(function() {
var Program = {
    main: function() {
        window.removeEventListener('load', mainEventListener, false);

        var observer = new MutationObserver(function(mutations, observer) {
            // y'know what? MutationObserver sucks.
            // it doesn't give every modified node, just the top of a tree of modified nodes
            mutations.forEach(function(mutation) {
                Array.prototype.forEach.call(mutation.addedNodes, Program.processImgDescendants);
            });
        });

        observer.observe(document, {
            subtree: true,
            childList: true
        });

        Program.processImgDescendants(document);
    },

    processImgDescendants: function(node) {
        if (!node || !node.querySelectorAll) {
            return;
        }

        var imgNodes = node.querySelectorAll('.post-text img');

        Array.prototype.forEach.call(imgNodes, function(imgNode) {
            Program.processNode(imgNode);
        });
    },

    processNode: function(node) {
        if (node.tagName.toUpperCase() !== 'IMG') {
            return;
        }

        // walk up the tree until we reach the main post div, we don't care what's beyond that
        var parent = node;
        while (!parent.classList.contains('post-text')) {
            // if this image is already within a link, don't touch it
            if (parent.tagName.toUpperCase() === 'A') {
                return;
            }

            parent = parent.parentNode;

            // have we made it all the way to the top? we're not in a post!
            if (parent === null) {
                return;
            }
        }

        // ok, now we know the node is an unlinked image within a post
        var link = document.createElement('a');
        link.href = node.src;
        link.target = '_blank';
        node.parentNode.replaceChild(link, node);
        link.appendChild(node);
    }
};

var mainEventListener = Program.main.bind(Program);

window.addEventListener('load', mainEventListener, false);
})();