Click on the top Tablet border to rotate vertically.
NOTE that Flash is not going to work on the Tablet, even though you might see it working here.
You can preload a page or set portrait mode by passing using URL parameters, like this: http://tablet-emulator.org/?url=google.com&portrait
Pages in portrait mode are scaled to 75% by using CSS3 transformations, which work best in Firefox 3.5+, Opera 10.5+ and Chromium 5+.
The reload button on the Tablet address bar also works.