CSS Stylesheet Editor

I have the CSS Stylesheet Editor under my “Appearance” tab on my Dashboard, but I am not able to click inside the box and edit the text. I was able to do this momentarily, but now the box has frozen up and I cannot even select text in it. I am using IE 10 on Windows 7.

Has anyone had this issue and been able to resolve it? This is a relatively fresh install – the only thing I did was to install the “Responsive” theme and associated widgets, and the Jetpack.