Controlling iTunes with keyboard controls

On my Bluetooth keyboard are Play, Forward, Backward, etc. buttons, which, in the past, I have been able to use to control iTunes even when it is not the active window. Ever since I had to reinstall iTunes, however, the controls only work when iTunes is the active window, which is an annoyance when I want to control my music while I'm using Firefox or other programs. Can I get help in reverting this back to the way it was?