In principle, forms of entertainment that are free of ḥarām elements such as gambling or free-mixing of the genders are permissible provided they do not lead to neglecting responsibilities or wasting excessive time or resources.^[1]

As such, watching and lighting fireworks (safely) are both permissible given the above conditions.

And Allah knows best.

Ml. Ameen Shariff
Student, Darul Iftaa Chicago 

Checked and Approved:

Mf. Abrar Mirza 
Head Mufti, Darul Iftaa Chicago