Wow, I love it. Brilliant visualisation of the browser's rendering process. This could even be useful in practice for working out how efficient your markup/CSS is. People with slower devices will appreciate shorter rendering times. Now if only there were instructions for how they came up with these. (I'm guessing it's some special debug mode for the developers, so you'd have to compile Firefox with some patches)

I expected this article to be about soldering things in a toaster oven.

http://www.instructables.com/id/Toaster-Oven-Reflow-Solderin...

CSS would become so much easier to learn (and teach!) with a tool like this.

Actually, "would" should probably be "will", since this tool is so useful.

more reflow action: http://gyu.que.jp/sjs2007/clip/M_reflow.wmv

and the main page (linked from comments) http://gyu.que.jp/sjs2007/