Why can't they view the upside down text?

I need a little bit of help figuring something out. I’m using a website to write upside down text on facebook, but a couple of my friends say that they can’t see the text on their computers. I see the flip text just fone on my computer, and so can a whole bunch of my other friends. What could be causing these few people to not see the text? They say the letters show up as little sqaures. They’re using Internet Explorer and Windows XP, if that helps.

¡ʇı ǝʇɐıɔǝɹddɐ ʎllɐǝɹ ı – dlǝɥ ɹnoʎ ɹoɟ sʞuɐɥʇ