What actually happened was:
If you shoot a fireworks rocket from a crossbow, shoot to mob and it does not hurt him, fireworks does not explode in them. Fireworks slides on the ground until it explodes.

What I expected to happen was:
I waited for the fireworks rocket to explode where it hit (mob) and caused regular damage to the crowd it was shot at.

Steps to reproduce:
1. Put a crossbow in your mainhand.
2. Put firework rockets in your offhand.
3. Load the crossbow.
4. Fire the loaded firework at a mob in an open area.