This is only happening on instagram and twitter right now. Whenever I go on twitter, where someone put an emoji, only a empty box will be there. And when I click on someones instagram, all their pictures show up as grey boxes. When I went on firefox there was not a problem with instagram photos, but I still couldn't see emojis. I already tried changing my DNS settings, and made sure "display images when the page opens" box was checked in preferences. Also, I just downgraded from mountain lion back to snow leopard, and this was when it started to happen.