gistfile1.html

<style>
	@font-face {
		font-family: 'foo';
		/* this font only contains the glyphs 'f' & 'o' */
	}
	@font-face {
		font-family: 'bar';
		/* this font only contains the glyphs 'b', 'a' & 'r' */
	}
	.test {
		font-family: 'foo', 'bar', sans-serif;
	}
</style>

<p class="test">foo</p>
<!-- 
	Firefox (3.6) and Opera (10.6) will load fonts 'foo' and 'bar', it sees that an element matches a style
	with those fonts & loads them.
	
	Webkit (chrome 5) is clevererer and only loads 'foo', it won't try and load 'bar' unless
	chars are used that don't exist in the 'foo' font.
	
	IE will load fonts 'foo' and 'bar' regardless of any usage on the page
-->

I've proposed some changes over at https://bugzilla.mozilla.org/show_bug.cgi?id=579916 - I've made a similar report in the trackers for Webkit, IE & Opera.

I looked at IE9 by the way, it behaves the same as Firefox & Opera in the case above. However, it also blocks page rendering worse than IE6-8. Hopefully they'll fix that along with the downloading-too-much issue you filed a report on.