[boot] - Fix signup form ui bug in firefox.

Fix float elements from this:

![screen2](https://cloud.githubusercontent.com/assets/796960/3430130/091bf1f0-005e-11e4-9727-17104d873561.png)

To this:
![screen1](https://cloud.githubusercontent.com/assets/796960/3430128/022ef1f8-005e-11e4-82b9-0537f300b09a.png)