Sleazy Fork is available in English.
Can work on almost any webcomic/manga page, preloads 5 or more pages ahead (or behind), navigates via ajax for instant-page-change, lets you use the keyboard, remembers your progress, and it's relatively easy to add new sites
< Opiniones de Webcomic Reader
I have made a fork of this script which fixes that issue amongst others. It is available at https://github.com/anka-213/webcomicreader and at https://openuserjs.org/scripts/anka-213/WebcomicReader.
batoto change their page reader url
Well, batoto changed the page url so the script won't work there anymore.
The fetching method also might be different from before.