i think michael would be best for writing it up, although it's even simple enough for me to understand, so here goes a try
1. you have to start with a base image for the background, it needs to be light enough to let the background come out, i took several this night from the same spot, with varying amounts of exposure time to give me a range to pick from. the old f11, iso 100 and shutter open in differing time lengths. you do want to capture some detail. you do this from where you are going to shoot the fireworks from, and you do not change the tripod angles at all when you shoot the show
2. shoot your fireworks shots, keeping in mind you want as dark a background as possible, so your burst shots are now very brief, a couple of seconds a lot of the time
3. i process my shots in lightroom, and i have what i think is a pretty decent fireworks preset that i have tinkered with over the last 4 years and gotten to where i like it, i cull out the rejects and then just group apply it to the remaining shots
4. select and fine tune your base shot
5. in lightroom select the 2 photos, base shot and the burst shot you want, click on photo, click on edit in and select whatever version of photoshop you use to open the 2 photos
6. click on the base shot, this will open it as the background layer
7. command a
8. command c
in windows i believe this is control instead of command
9. now click on the fireworks shot, this now opens up as layer 1
10. command v
click on normal to get the drop down
click on lighten, default is 100 % opacity, you can adjust to taste
that's it, you should now be seeing the combined photo in the ps view window
i have been exporting from lightroom as tiff's, so for me right now it takes a minute for both to open up as the working files are currently in adobe dng
i will in the near future be abandoning dng and working in raw so as not to lose any file details. this new laptop is muscular enough to handle these files and i really see a speed difference
i still have 2 drobo slots open out of 4 so when the time comes i can really boot up my storage as this drobo will recognize drives up to 12 tb in size.
so i am now saving the finished file as a tiff, importing back to lightroom and converting to jpeg when ready to upload to my phanfare site