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
Bugs on mangabird.com
All pages on mangabird.com are displayed incorrectly.
example:
http://www.mangabird.com/manga/kingdom-manga
http://www.mangabird.com/
http://www.mangabird.com/alphabetical/O
(Posted here: http://openuserjs.org/scripts/ameboide/Webcomic_Reader/issues/Bugs_on_Mangabird.com)