Noting the generator was Frontpage, thought I'd check it out in IE9, where it works fine - even if you use dev tools to change the document mode to standards.

Interesting. The font tags appear to have been closed with </font color>. What's weirder is that there are no line breaks so it kind of seems as if an IDE did this.

The generator is listed as frontpage 5.0.

Plus it seems to 'split' tags resulting in things like this: <width="25%" align="left">

Not very pretty.

Absolutely hilarious: http://imgur.com/UogN3lU

I feel the browser is trying to tell me something about my afternoon: http://imgur.com/UzgATO1

So, what's going on here? Why does the font size keep increasing like that from not closing tags?

They are using EM's for font-size, which is a relative measurement.

This means that if you set your font-size to 1.5em, and you have an element inside (as a result of the unclosed tag) also set to 1.5, the one inside is set to 1.5 times that size (or 2.25 of the original 1em). That cascades on and on and on and...

It's missing closing heading tags (h2, h3). So each heading contains a heading contains a heading... headings all the way down.

EDIT: And yes, the heading tags have relative font sizes, as cleverjake pointed out.

Utterly hilarious.