"Fireworks" is well-known for its music video. In the official music video, Katy Perry sings through four or five different scenarios of individuals overcoming their fears and showing their truth inside. These sequence are memorable because CGI-applied fireworks emit from the chest area of each said individual.
As for the song itself, it is incredibly upbeat and uplifting to hear. I read it is a less serious version of Christina Aguilera's "Beautiful" and I fully agree: there are no vague connotations, just a straightforward self-esteem enhancing song. It should be heard by anyone who is feeling down for whatever reason.
The specific lyrics I like are:
"If you only knew what the future holds, after a hurricane comes a rainbow. Maybe you're reason all the doors are closed, so you could open one that leads you to the perfect road."
The first line reflects on the fact that most difficulties are temporal and short-term. Most challenges that come our way can feel overwhelming at the time of happening; in other words, we exaggerate their affects and future implications. In reality, these challenges are negligible in the grand scheme of things (if you are a Christian, suffering is somewhat necessary to realize our dependence and need for God). But the problem is that we forget this while faced with the problem/challenge. Perry's line brings a reminder that after every hurricane -- a powerful and often destructive natural phenomenon-- comes an elegant rainbow. The rainbow represents the calm and beauty that follows destructive occurrences like hurricanes.
As for the second line, it speaks of the closed-doors we may encounter in life. Examples range from rejection from a significant other to the inability to get a job. We are often faced with such closed door analogies in life -- which can be very damaging to our self-esteem and confidence in our own abilities. But perhaps the reason for these closed doors is so we can eventually open the correct one that "leads you to the perfect road". The key is to keep trying and not give up; keep trying your hand at the different doors in front of you. It's far better to have doors to try than none at all.