This is easy. I horizontally flipped the "Show Thumbnail Pane" button as well :D
CODE
// ==UserScript==
// @name EH Relocate MPV Thumbnails
// @namespace https://github.com/Mayriad
// @version 1.0.0
// @author Mayriad
// @description Recolate MPV elements to move the thumbnail pane to the right side
// @include https://e*hentai.org/mpv/*
// @run-at document-start
// ==/UserScript==
;(function () {
const mpvRelocationStyles = document.createElement('style')
mpvRelocationStyles.type = 'text/css'
mpvRelocationStyles.id = 'mpvRelocationStyles'
mpvRelocationStyles.textContent = `
div#pane_thumbs { left: auto; right: 0px; z-index: 1; }
div#pane_images { left: 0; }
div#bar2 { float: left; }
div#bar3 > img[title = "Show Thumbnail Pane"] { transform: scaleX(-1); }`
document.documentElement.appendChild(mpvRelocationStyles)
})()
QUOTE(sartan @ Sep 24 2019, 01:15)

couldn't see one in the script thread nor find an option for this in settings, hopefully this is the right part of the forum to ask.
This is the right place, but yeah, you will not find an existing script that addresses such a specific and uncommon need. Why do you need this anyway? Because it is more natural to have the scroll bar on the right side? Or just personal preference? I think it is not a bad idea, so I will add this to my master script, too.
QUOTE(sartan @ Sep 24 2019, 01:15)

bonus question: is there any good reason scroll click for mouse movement to scroll up and down is disabled in that mode?
There is no good reason, because it is not disabled.
You can auto-scroll the thumbnails pane just fine, and the main image pane is actually already shorter than your screen, so there is nothing to scroll. It appears to move when you scroll, but it is actually using specialised functions to create new images, destroy old ones and shift them into and out of view in the background. It is like your physical computer monitor: when you scroll, the screen will show you different stuff, but the physical monitor itself is not that long and certainly cannot be scrolled. This is the logical solution because making the main image pane an ordinary scroll-able document means it can potentially hold up to 2000 big images at once. You(r computer) will not like this.
Sigh, this paragraph above actually took longer to write than the code.
This post has been edited by mayriad: Sep 24 2019, 04:27