I am using Bootstrap v2.3.2 and jQuery Datepicker v1.10.0,
On a modal I am trying to make use of the datepicker and it is appearing behind the modal on Firefox and
This answer covers the issue.
This is a z-index issue. Normally applying a higher z-index via CSS would work, however jQuery resets the CSS each time the Datepicker UI is drawn.
z-index
The solution re-applies the CSS each time it's drawn by using the beforeShow property.
beforeShow