Could be it's timing out somehow before fully loading. I know Internet Explorer won't activate the 'save as' option until it's all there. Perhaps someone in the Mac forum can clue you in on where the browser cache is or barring that just search the whole drive. If that doesn't work, I'd try emailing the guy and see if he can give you a direct link. Worst case scenario, I suppose you can just do screen captures scroll and snap 'til you've got the whole image and then stitch it back together in a paint program - bit tricky with overlap but better than nothing.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken