[Reboot] Support for transparent button backgrounds in firefox

Created by: oleersoy

Hi,

SuitCSS's base module contains the following snippet to support focus styles in firefox when the background is transparent:

/**
 * Work around a Firefox/IE bug where the transparent `button` background
 * results in a loss of the default `button` focus styles.
 */

button:focus {
  outline: 1px dotted;
  outline: 5px auto -webkit-focus-ring-color;
}

Would this be appropriate for bootstrap to include?

Cheers, Ole