Minor fix to custom drop down in Firefox

If a custom drop down is displayed as inline, it doesn't align with the text property in FF. Eg:
```
<form class="custom">
   <p>Bla bla bla <select></select> bla bla bla</p>
   <style> .custom.dropdown { display:inline-block; width:100px; } </style>
</form>
```
As per http://stackoverflow.com/questions/5373400/why-does-setting-line-height-for-one-of-two-inline-block-sibling-divs-effect-bot ``vertical-align:top`` fixes it.