only show scrollbars if there is a need to scroll in firefox

Unsure if the overflow was intentionally set to scroll, but as it is both horizontal and vertical scrollbars show up regardless of where there is a need to scroll. 

BEFORE
![image](https://f.cloud.github.com/assets/41799/2403121/e6821ee6-aa2a-11e3-94c8-f99e914f55e1.png)

AFTER
![image](https://f.cloud.github.com/assets/41799/2403106/cf443886-aa2a-11e3-8aba-807c87ed10e9.png)