fixes firefox user image disappearance

User image doesn't appear in FF because the `height: 100%` applied to `a` element doesn't get expressed. Setting height / width explicitly to match the wrapper. Tested in FF and Chrome on Linux.

![before](https://f.cloud.github.com/assets/99194/1335576/e486efb6-35ba-11e3-8a7f-41a87059aeff.png)

![after](https://f.cloud.github.com/assets/99194/1335577/e5efa046-35ba-11e3-998a-3f8806f68e89.png)