Just find out how to switch window within the same program in Mac OS X. By default, you press Apple + Tab to switch window for different program (ex: switch from Firefox to Thunder and vise versa).
If you want to switch window within the same program (ex: I have 3 Firefox windows and want to switch among the 3 firefox windows), you can click on Window -> Select the Window name you want.
If you want to switch window within the same program using shortcut key, you can press Apple + ` key (` key is just located on top of Tab key).
Just hold Apple key and press ` key to change the application window.