Just a thought.
When the discussion about W8 was talking about downloading the OS, I looked at the download link. It seemed to offer the download with no further ado, and I cancelled it a bit sharpish.
Could this green bar in the FF task bar button have been showing the download in progress, because when it got nearly to the end, and I had not found a single clue as to what was going on, I panicked and ran CCleaner. It cleared the bar.
Needles to say, that would have destroyed any download and the download list by doing this, so I've left myself with no evidence except the convention of the bar itself.