chrome-specific padding for the compat selector (bug 1093936)

## Old

https://www.dropbox.com/s/koula33kr2qqnww/Screenshot%202014-12-02%2014.30.20.png?dl=0

## New

![screen shot 2014-12-02 at 2 40 51 pm](https://cloud.githubusercontent.com/assets/674727/5272407/71c8f9c6-7a31-11e4-8249-a6d1b349258d.png)

It's hacky, but it seems to work.
you added `-moz-padding-start: 10px;` in the [original commit](https://github.com/mozilla/fireplace/commit/2ead6e8#diff-3aae7cac9542dcbeafaf7cb3b05afe45R44). do you remember why? `padding-left: 10px` seems to work in Firefox and Chrome.