Firefox v48.0.2 incompatibility

Hey,
Love this code. Noticed it wasn't firing on Firefox 48.0.2

It was getting the vendor prefix as '-ms-' instead of '-moz-'.

I updated line #20 to the below (from https://davidwalsh.name/vendor-prefix)

``` javascript
pre = (Array.prototype.slice
.call(computed)
.join('')
.match(/-(moz|webkit|ms)-/) || (styles.OLink === '' && ['', 'o'])
)[1];
```