Firefox/IE handling css "right" property differently?

I have a div like this...

<div style="position:fixed; top: 60px; right: -51px;">
      <form>
         ....
      </form>
  </div>

In Chrome/Safari, it perfectly positions a little search box at the top right of the screen.

In firefox/IE, the top is correct, but the position to the right isn't tight enough to the edge (looks like around 100px).

Here's an example: http://codepen.io/d3wannabe/pen/LZNVqe

Hugely appreciate any thoughts from anyone who knows why this might be happening!