itch.io

This might not look and read as you imagine it. But here, try it out. Either copy paste the middle in console of your browser or put the whole thing as the url of a bookmark and activate the bookmark on a page with a thread.

This is not recursive for replies, but you do not read lines from bottom to top either. And of course you still need to go to the last page of a lengthy thread.

javascript: (() => {
    const c = document.querySelector('.community_post_list_widget'); if (c) {
        [...c.children].forEach(n => c.prepend(n));
    };
})();

--

Or simpler yet. Use a style addon like Stylus and apply for itch.io. You can probaly use that for replies somehow to reverse them too, if you use the proper selectors.

.community_post_list_widget {
    display: flex;
    flex-direction: column-reverse;
}