It's not.

div#whws { font-size: 100cm; height: 18939.5em; line-height: 1.0; }

Yes it is:
div#whws { font-size: 100cm; height: 18939em; line-height: 1.0; }

And why highest and not longest or tallest?

There's no such thing as the longest website. If you create a page that's x pixels long, I can always add an image (or something else) and now it's x+h pixels long, h>0.

lol @ Ionut =)

Aah, but there is a web site that is even taller: deepskyfrontier.com/

Unfortunately, I am not able to resolve the address right now. But it's referenced on your own Carnival of Web Extremes, Phillip, which is actually where I think I saw it first: blogoscoped.com/forum/62264.ht ...

Wouldn't it be "tallest"? The highest would be aboard the ISS or some satellite.

I always wondered wether satellites have IP addresses. What would be the ping-times? Transmission speed? And are they running Apache or IIS?

Ionut:
Firefox doesn't support websites longer than 18.939583 kilometers, so the website says at the buttom. (Apperantely, u didn't scroll down enough), and they say:
If you can come up with fixes or an even higher element, whose formatting is broadly supported, email info at worlds-highest-website.com. Most likely, there’s some reward. And otherwise, if it’s found, it’ll be used ;)

Let's settle this. Somebody print it out and measure it.

Heh. No takers?

guess not..
it can probably cause HP to go bankrupt :P

[Moved from "Worlds highest website" – Tony]

worlds-highest-website.com/

Yea.
And IE vs. Firefox on the bottom.

Ooops. Sorry. :/