Not sure why, but the full-size original image for this post has problems with some browsers, including Firefox 3 and Google Chrome, which (for me at least) claim that the file has errors and cannot be displayed.
I've had this problem a few times before in Firefox (with other images, not on this site). From experience, I think it has something to do with the image-loading process being interrupted. (I've forgotten how to replicate this error.)