Dropdown menu in justified button-group

This is a firefox issue. I tested it on firefox latest (28.0).

It seems that dropdown-menu in justified button-group appears at the far left of the group.

Check the problem in [Bootstrap site](http://getbootstrap.com/components/#btn-groups-justified).

![ff28-btn-group](https://cloud.githubusercontent.com/assets/7236465/2729097/f4b5627c-c602-11e3-9023-ce8a4c3fed5c.PNG)