Shows just fullsize Image with hotkeys & without pop-ups on many image-hosting sites
Uploader is most likely in an iframe, Handy Images also work in frames if their urls are matches, inspect element, its url might be needed to add into excludes
Can you add it into excludes?
added
I can't upload photo in imagetwist.com
I have trouble uploading photo in imagetwist.com.
I tested with clean Firefox+Greasemonkey+HandyImage.
http://imgur.com/a/kQNU1