ReplaceURLs(GoogleImages).user.js

// ==UserScript==
// @name          ReplaceURLs(GoogleImages)
// @namespace     https://ashiato1.blog.fc2.com/
// @description   Replace URL with original image URL in Google Images
// @author        tomato111
// @version       0.0.15
// @downloadURL   https://gist.githubusercontent.com/tomato111/681d634ded1a9bd3107e2baf60460a35/raw/ReplaceURLs(GoogleImages).user.js
// @updateURL     https://gist.githubusercontent.com/tomato111/681d634ded1a9bd3107e2baf60460a35/raw/ReplaceURLs(GoogleImages).user.js
// @match         *://*/search?*udm=*
// @match         *://*/search?*tbm=isch*
// @run-at        document-start
// @grant         none
// ==/UserScript==


(function () {
    function replace_url(a) {

        const imageURL_RE = /[?&]imgurl=(.+?)&/i;
        const href = a.getAttribute('href');

        if (imageURL_RE.test(href)) {
            let imageURL = decodeURIComponent(RegExp.$1);
            imageURL = imageURL.replace('-origin.fc2.', '.fc2.');
            a.setAttribute('href', imageURL);
            a.onmousedown = function () { /*nop*/ };
        }
    }

    function replace_on_mouseup(nodeSnapshots) {

        for (let i = 0; i < nodeSnapshots.snapshotLength; i++) {
            const a = nodeSnapshots.snapshotItem(i);

            a.addEventListener("mouseup", function () {
                //console.log("mouseup", a);
                replace_url(a);
            }, { once: true, capture: true });
        }
    }


    document.addEventListener('DOMContentLoaded', function () {

        const a_xpath = '//a';
        const obs_target = document.querySelector('div#islrg') || document.querySelector('div#rso');

        const nodeSnapshots = document.evaluate(a_xpath, document, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);
        if (nodeSnapshots.snapshotLength) {
            replace_on_mouseup(nodeSnapshots);
        }

        const observer = new MutationObserver(function (MutationRecords) {

            MutationRecords.forEach(function (Record) {
                Record.addedNodes.forEach(function (node) {
                    if (node.nodeType === node.ELEMENT_NODE && node.tagName === "DIV") {
                        const nodeSnapshots = document.evaluate('.' + a_xpath, node, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null); // .== self::node()
                        replace_on_mouseup(nodeSnapshots);
                    }
                });
            });

        });

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


    }, false);

})();

If it is working properly, middle-click on the image to open the original image.

Middle-click [1] - the webpage [2] still opens. Instead http://img1.reactor.cc/pics/post/full/Санкт-Петербург-погода-Ведьмак-(The-Witcher)-фэндомы-4241887.jpeg

[1] https://www.google.com/search?as_st=y&tbm=isch&hl=en&as_q=ведьмак болото&as_epq=&as_oq=&as_eq=&cr=&as_sitesearch=&safe=images&tbs=isz:lt,islt:2mp#imgrc=TVyonUsCBECrgM
[2] http://reactor.cc/post/3357630

Firefox 78.0b2 (64-bit).

Even if you middle-click in the red square?

I can't find the cause.

Now I understand how this script works. Yes, thanks, everything is fine (Mozilla Firefox 79.0b4 (64-bit), Tampermonkey 4.11.6114).