Malformed fonts in Firefox

[Justin Yang]

Hi,
My box runs on a Intel Sandy bridge chip, and previously I've updated my  
xorg and any related ports to the latest one in experimental xorg repo via  
svn (with KMS enabled). However, there are some malformed fonts shown in  
the Firefox (including firefox-esr and linux-firefox) unexpectedly  
sometimes, as shown in the following picture, and I couldn't figured it  
out currently. However, the fonts are really normal in other browsers,  
say, Opera and Chromium. So, what should I do to deal with it? Thank you:)

Malformed fonts in Firefox:
http://i48.tinypic.com/icteo7.png

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Best Regards,
Justin Yang