Firebreath is not suppose to be listed in the options to select. All of the other dragon skills should be, however, as long as you have invested any skill points or are wearing any dragon armour with a particular bonus.
Speaking of which, maybe try changing equipment around, and see if that resets whatever the problem is. There are a couple pieces of armour in the battle tower chest, if you didn't notice after returning from the first battle.
Try emailing support@larian.com, with a description of the problem (including game version, etc) and maybe attach a save.
In XP the saves are in the folder
C:\Documents and Settings\ %username% \Local Settings\Application Data\Divinity 2\Savegames
or in Vista / Win 7
C:\Users\ %username% \AppData\Local\Divinity 2\Savegames
You may need to set Windows Explorer to show hidden files and folders (
XP, Vista,
Win 7).
