This is in fact a failed experiment, failed mainly because it doesn't work in most cases. I made a version that doesn't use browser windows, but it sucks.
Obviously won't work where there are no windows :> (mobile, dwm etc)
Will only work on FF and chromium based browsers (not on linux though in my case, it was unplayable...), because other browsers (like midori) make it impossible to do such crazy things with browser popup windows... (in case of IE, because they were used mainly for malicious purposes in the past).
Browser popups can't be smaller than 100x100, but often even 100px is too small
Some window managers may make it harder for you to control the window position (via snapping etc), see next point...
Movement may not be smooth anyway, it's better when you drag the window content area, not the titlebar, as the titlebar drag may not work at all in some cases.
This is more annoying than you'd imagine...
Look at the code at your own risk, this was speedcode and omgwhyamicodingthis style project :>
How to play (deluxe version of the tutorial):
Start the game.
Drag The Browser Window in the direction pointed in by the arrow until you "see" the next arrow (or run out of time :)
If the arrow is white, it means you haven't "seen" enough - drag around until the arrow turns #7ff
Go to step 3.
Technically you can't arrive here, so I have a theoretical question: is this step a part of this tutorial? Hmm...