Ender Dragons firebreath attack deals no damage at all,
Steps to Reproduced:
1. Create a world and enter the End dimension
2. Make sure your on survival
3 Destroy all Crystal for the dragon will likely to perch.
4. Go to the bedrock nest and camp or when the dragon is perching simply go to the nest, this will make sure that the dragon will fire its breathe attack
When the dragon fires out her dragons breathe, go towards it and it deals no damage at all.
The acid should damage any entities when entering the dragons breathe dealing 3 damage or 1 1/2 hearts.