Okey, like I said yesterday it was my fault. Apologies. I have unchecked the box "Allow pages to choose their own fonts, instead of my selections above".

This is the first time it bites me in the ass though! It produces a shadow and lighting effect on the letters which is really distracting: http://imgur.com/qYkeh.png

I'm ashamed I didn't put this in my original post!

I can't recreate it on my machine at home although they both run the Debian testing branch and use Iceweasel. I'll let you know tomorrow but it's probably PEBKAC.