I found some stickyness on Firefox 18. I've deployed a fix but I put a 24 hour cache in front of the page before posting it to hn so it'll probably only update for you this time tomorrow.
Fox 18 on XP here and I can't get anything to work, either. Mouse scrollwheel, spacebar, arrow keys all do nothing.
In addition, I don't know if you're using any light gray for visual cues. That's a problem. My screen is crap with shot contrast and light gray tends to become white that I can't see. I wish to hell everyone would stop using light gray everywhere.
Windows 7 64bits and a standard usb mouse. I haven't tested the bookmarklet though, I was talking about the website itself: scrolling doesn't do anything and pressing H doesn't display anything either. I went to check the "Alice in Wonderland" ebook on your main website and everything seems to work perfectly there.
