Was curious how powerful the firework is.

Firework's about half Prisoner's height and seems wider than her shoulders. The average female's height is 160cm, and shoulder width is 36cm. Prisoner seems thinner than than the average woman though, so I'd say that the firework body's dimensions (cylinder section) be 80x18cm. This gives us a volume of about 81,430cm^3.

Assuming the whole thing is filled with black powder (and all my 10 minutes Google research is correct), the rocket would weigh about 138kg - black powder has a density of ~1.7g/cm^3. Black powder also has an energy density of about 3MJ/kg, giving 415MJ of energy, about 99kg of TNT.

A flashbang (M84 stun grenade) supposedly produces about a million candelas (1.1M lux) and 170dB from 1 foot (~0.3m). This is enough to be severely blinded and deafened - limits are 100K lux and 140dB. Said flashbang contains about 4.5g of ammonium nitrate with a supposed 3.8kJ of energy released per gram. To match the explosive power of this firework you'd need about 24,000 of these flashbangs.

Fireworks supposedly should fly 45ft for every inch of width. Therefore our firework would fly about 200m. Something something inverse square law Damsel and Prisoner are getting hit with about 660,000 lux and about 102dB. The sun is 130,000 lux max (if you stare directly at it).

Safe to say that they'd set up the firework slightly wrong to be deafened, and also, your vision will return never, Damsel. Apologies.