Firefox does not show button images

Hi, I did have Firefox v28 and recently upgraded to v29 (very nice btw). Both versions have the same issue.

If I go to the Twitter website and log into my account, I can see odd looking boxes with numbers where an image of the button/icon should be. I can click on it and it will do what it is supposed to do apart from look correctly.

I have started Firefox in safe mode and it made no difference. I’ve tried Facebook, Youtube, BBC and a number of other sites and they seem to be ok.

Any ideas?

On wordpress I am able to fix that by allowing the webpage to use its own fonts (see below). This does not work on the twitter page though. I suspect its something related to that.

That did it, nice one.

I had the option disabled and I had set up my serif and sans-serif fronts as Deja Vu mainly. I also tried going back to the default fonts to see if that helped

Many thanks.