Thanks for the information! I first noticed the improvement in Aurora and Nightly builds, and was wondering what they did to fix the problem.

Here is some more information I just found for anyone interested:

Main bug report:

https://bugzilla.mozilla.org/show_bug.cgi?id=661471

The two new preferences:

gfx.font_rendering.cleartype_params.force_gdi_classic_for_families

gfx.font_rendering.cleartype_params.force_gdi_classic_max_size

And a post talking in detail about the issue:

http://blog.mozilla.com/nattokirai/2011/08/11/directwrite-te...