Bug 1093762: Set equal width for mobile buttons

Before:

<img src="https://camo.githubusercontent.com/db1eff65f32604bc32b1d03a6ef97889995467c1/687474703a2f2f692e696d6775722e636f6d2f7762586f514e342e706e67" alt="A vertical column of buttons, each with a different width." />

After:

<img src="http://i.imgur.com/ABNz12o.png" alt="A vertical column of buttons with equal widths." />