Whether a box is checked or unchecked, it shows as a solid red square. This
makes it rather frustrating to interact with option on many sites.
Here is an image of the problem:
http://chunk.io/bard/03a3263f74ed47418e5077e738662c5a
It happens on multiple sites and even in some of the icecat preferences
themselves.
another image: http://chunk.io/bard/d943f262c1b148ab875e49c08df683a3

It's been an issue for a while so I'm afraid I can't easily track down the
issue to a recent update or anything. I complained in IRC a few times but
have been putting off sending an email about it.