the whole part of the css that remove outline of dropdown menu is a hack, because 
```css
select {
  outline: none;
}
```
does not work on Firefox.

The outline color is decided by text color in `select` element, however we do want to keep text showing in `select` element. That's why we add `text-shadow: 0 0 0 #000` to hack it.

http://stackoverflow.com/questions/3773430/remove-outline-from-select-box-in-ff