The perspective from the bridge isn’t quite right.
The key to MK fireworks (any MK fireworks) is that you need to keep the castle fairly in front of you. This is because there are really two different displays happening at the same time. There is the castle display, all the stuff launched from and next to the castle which is low flying; and there is the high flying aerial display that is launched just outside the park. The way it’s designed, it all falls together as one so long as you are no more than 5 degrees off the center axis of the castle.
So, anywhere on Main Street, but you’re better if you’re even with or in front of Casey’s Corner/Ice Cream Shoppe. You’re good all the way to the popcorn stands. Any closer and the castle starts to block the high stuff. On the left, you’re good all the way to Crystal Palace, but don’t go so far as the bridge and the best place is that little circle where the photopass photographer is always stationed. On the right, you’re good to the Noodle Terrace (which itself was a good viewing spot because Tink does fly right overhead, but you now have to pay for the honor) and that lower seating area associated with the Plaza. There is also a path on the right just next to the popcorn stand that curves back to the main spoke into Tomorrowland that again puts you directly under the wire. Main Street Station is a nice place to watch from as is the flagpole circle, although that spot can be a little like having blinders on because you are looking down the street at the castle with buildings on either side. Outside the park two of the best places are the ferry landing in the TTC and Sunset Point at the Poly as well as the Poly’s beach, although again, you are starting to get off axis.
I can’t stress how important it is to keep the castle in in front of you. If you don’t, the whole illusion falls apart. Perhaps the best example of this is viewing from California Grill where you can plainly see the two different parts and how big the physical separation between the two displays is.
Illuminations. The plaza at the head of World Showcase Lagoon between K Mart and WalMart, lantern 1, the bridge between WS and Mexico, lantern 4 near China, the little pier in Germany, the big plaza in Italy especially if you can get onto the section that is over the water, Japan to the right of the arch in the water or looking through that arch and also the balcony in front of Tokyo Dining (this is partly obstructed by the arch), the border line of Morocco and France (I think lantern 13), the bridge between England and France, and parts of Canada that aren’t blocked by trees.