The same thing happens in IE. If I close Firefox, open IE, log on to my account, come here, hit the Link, it runs fine. Now go to Firefox, paste the link, up comes the error message in place of the figure.

This is a bit subtle, so I can appreciate your confusion. To display a plot like a ListPlot in the cloud front end (the browser) we need some extra information from the kernel that isn't needed for a notebook displayed on the desktop. When that information is not present, a kernel evaluation is needed which requires that a notebook be interactive. There are two ways you can end up with a graphic in a notebook that needs a kernel evaluation. The first is to create that notebook on the desktop and upload it to the cloud, because we don't currently process that notebook when it is uploaded. The other way is to copy a cell with a graphic from one cloud notebook to another. I'd say that this second case is just a bug and I'll see what we can do to fix it. The work around in your case is to generate the graphic again in the notebook you want to share rather than cutting and pasting it. You can also just convert the graphic to an image, which, since you are sharing a static notebook is good enough because one can't resize graphics in static notebooks anyway (that requires a kernel evaluation and therefore interactivity to be allowed).