I've run into an issue with Firefox. Check out the example: http://codepen.io/anon/pen/BuLhF.
Basically, with the font Poiret One, embedded with Google fonts, the letter ō
doesn't render properly in Firefox but in Chrome it is ok.
Edit:
Screenshot: https://docs.google.com/file/d/0B58rXlxeBUsIMXo1MnJrRFczbFk/edit?usp=sharing.
Moreover, on Virtual Machine Ubuntu, Firefox is displaying it ok. The host Windows 7 has this problem.