On my Powerbook monitor I can see all the seems. It's the black to black transitions that I'm seeing. If I turn the brightness on the monitor down enough, they go away.
I tried a levels adjustment... to make the dark colors darker.... setting the left slider to 10 made the seems go away.
I'll try to illustrate it here.
Here is your original at 100% in Photoshop. On my monitor, I can see the transitions where you've probably used the lasso tool to snag each fireworks burst.
Here, I've sketched the outlines of the rough transitions.
Here, I've adjusted the left levels indicator to 10... it makes the darks darker and pretty much leaves the bright fireworks alone. Now I no longer see the transitions.
And, here is your original with the levels adjusted - resized by flickr... but, you can make the same adjustment yourself. Or, I'd be happy to email you the file.
Hope this helps! This would look so cool printed big up on the wall!