Why is my Greek Open Sans displaying as serifed?

Question

I have built a website for a client http://charlesalexiou.com/ He wants some words in Greek. I used Open Sans, a Google font which includes Greek characters. It is a non-serifed font.
In Firefox it displays with serifs, both on a Mac, which I have, and a PC, which my client is testing the site on.
It is a WordPress site, which is optimised to use Google fonts, and I have no other issues with Google fonts I've used displaying just fine in Firefox. Even so, I added this code to the header: <link href='http://fonts.googleapis.com/css?family=Open+Sans&subset=latin,greek-ext,greek' rel='stylesheet' type='text/css'>
<meta charset="<?php bloginfo('charset'); ?>"> Just to be sure. I have also contacted the theme developers who are looking into it.
The Greek characters display properly in Open Sans in Safari and Chrome. They are serifed in Firefox (I'm using version 22) and IE10.
Is there anything else I can do? I desperately need to be able to have this website display perfectly across all browsers.
Thank you
Fergie

Answer 1

Hi Cor-el,
This is the Open Sans font and apparently it has Greek support:
[http://www.google.com/fonts/specimen/Open+Sans]
I did check before I selected it to use on the website.
Scroll down and you'll see Greek characters. It also has an extended Greek subset which I put a link to in the header of the website.
Cheers
Fergie