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
< Rückmeldungen aufManga Loader NSFW (unmaintained)
Same for exhentai: http://exhentai.org/s/f29853ce63/861652-1 (I assume you knew how to login exhentai)
Strange, it works fine for me in both chrome and Firefox with the latest versions. Maybe you've exceeded the bandwidth limit for the site? May or may not apply but this part of the ehwiki talks about issues with images loading http://ehwiki.org/wiki/Technical_Issues#E-Hentai_Galleries
Wait, it stopped working once I logged in. I'll look into it.
Fixed in v1.0.13
ehentai totally broken after recent update
http://g.e-hentai.org/s/b1f22dbc09/861719-1
it only loads 1 page. Tested in both Fx and Chrome.