Oldtimer said:You might get your wish. Races & Classes says this about shields: "Capable of turning away spear-thrust, arrow shaft, and fireball alike, ..."
So your fighter's shield will probably work against the dragon's breath weapon as well.
But what happens when the dragon's breath burns through your shield?
(No, I don't actually want rules on whether dragon's fire will burn through or melt a shield, no matter how much more realistic that makes the game. The last thing I need is my players complaining about all their wrecked magic gear every time a dragon breaths on them!)