The red sliders were also not working for me on OS X w/FF 3.6.3 though the slideshow and canvas mask demos were. Figured I'd try with Chrome and Safari and the red sliders didn't work there either.
After I reloaded the page in Firefox, they are working on all 3 browsers. Kind of baffling.
I know how frustrating "doesn't work" is as a bug report but I can't give a lot of detail since it all works now. When it wasn't working, "dragging" would just select text on the page. The "draggable" red sliders would not move.
If dragging would just select text on the page that means that the script was has not even initialized. Something was blocking the JavaScript to run at all.