How do I get rid of <select> element outline in Firefox?

Question

So here's a fiddle demonstrating the problem: http://jsfiddle.net/CVTrb/1/, click and select on any option, and then you should see a thin gray line appear that doesn't exactly sit within the <select> element.

Here's an image demonstrating this:

:

Answer 1

Credit to this post here: https://stackoverflow.com/a/18853002/1261316

select:-moz-focusring {
    color: transparent;
    text-shadow: 0 0 0 #000;
}

Answer 2

Add outline: none; to .form-dropdown