WebFont loaded from Google Font API looks awful in Firefox 3.6 on Windows only

For a site we're developing we've been using Lato from Google's WebFonts API. It works perfectly in every brow开发者_运维技巧ser (even IE), except for one very important case: Firefox 3.6 on Windows XP (haven't tested in Win 7 yet). The font loads and is displayed, but the characters look awful, like antialiasing completely malfunctioned.

My googling has found hits about problems with webfonts in FF4 due to a bug in the browser, but I can't find anything about 3.6. Is there something we can do to fix this?

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The reason Google's font looks like that has to do with a setting in the font's GASP table. This table toggles 'grayscale' and 'gridfitting' for ranges of sizes. I looked at the font Google is sending to your site and for sizes 0-13 grayscale is turned on. 14-18 is set for gridfitting, which results in black and white rendering. Then 19+ is set for both grayscale and gridfitting. I bet if you changed the size of the text to 13px, it would suddenly turn antialiased.

As for Font Squirrel fonts, we set the GASP table to render grayscale+gridfitting for all sizes above 4px.

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There seems to be a difference between Google webfonts and the same font downloaded from Font Squirrel, see this (unrelated...) question.

So I would try and use the version they have at Font Squirrel to see if that solves the problem.