How to get fireworks

• Level 1-2: Warp to World 2, 3, or 4
• Level 4-2: Warp to World 6, 7, or 8
• Level 4-2: Warp to Word 5 (Yes, there are two on this level)

The following detail came from this site.

Where to find warp zone #1 hidden in level 1-2

You will find the first Warp Zone located at the end of level 1-2. In order to reach it, you will need to ride the previous elevator to the top and then jump onto the brick ceiling. Run all the way to your right and you will find the Warp Zone. Enter the corresponding Pipe to skip to world’s 2, 3 or 4.

Where to find warp zone #2 hidden in level 4-2

This level contains two Warp Zones, one to level 5 located at the end of the level, and this Warp Zone that takes you to levels 6, 7 and 8 located in the middle of the level. To find this Warp Zone look for a high three-brick-long platform that is too high for you to reach, located across from the first elevator platform. There are some invisible blocks that you will need to make appear in order to reach the far left block, which contains a vine. You need to hit the invisible blocks from below to create a staircase allowing you to reach the Vine. To do this, make the first two lower blocks on the righter side appear. They will start to create a staircase. Then hop on them and break the two bricks above. If you haven’t already activated the vine, try to do so now, and then make the following invisible blocks appear if you need them to reach the vine. Climb the vine and you’ll reach the Warp Zone that can take you to worlds 6, 7 or 8 depending on which pipe you enter.

Where to find warp zone #3 hidden in level 4-2

To reach the final Warp Zone (note that you can only take one Warp Zone since both are on the same level), you will need to reach the ceiling from an elevator platform and then run all the way across it to the right, just like you did in level 1-2. This Warp Zone will take you to World 5.

From the screenshot shown on that page, it appears that the coin blocks have been relabeled with "25". I hope, at least, that this was the only "partially rearranged" issue in the 25th anniversary of a classic.