Sleazy Fork is available in English.
Loads manga chapter into one page in a long strip format, supports switching chapters and works for a variety of sites, minimal script with no dependencies, easy to implement new sites, loads quickly and works on mobile devices through bookmarklet
< Opiniones de Manga Loader NSFW (unmaintained)
Found newer script that works (including 8muses), since this one isn't updated.
I'm not affiliated with this script, but I found one that does the same job, and is up to date: https://github.com/TagoDR/MangaOnlineViewer
My suggestion is to click the settings cog on a given manga page, and set it to "theme: dark"; "default load: Never (manually)"; "show thumbnails" unticked.