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)
For some reason the script misses some pages on exhentai, loading a svg-data-url instead of an image.
(This especially seems to happen with longer galleries.)
data:image/svg+xml;charset=utf-8,...