It's just how the page loads.
The HTML code for the Wall'O'Fame pictures gets downloaded before most everything else on the page. So, if you were to stop downloading the HTML right after Wall'O'Fame, it would stay centered in the page because that is the way the browser interprets the incomplete code.
Since Firefox and Chrome frequently redraw the web page as data is downloaded, that is the flash you are seeing.
If you were on a 56k modem it might look a bit more "normal" since visual restructuring would happen with almost every web page.
