Firecrackers are an item that can be bought from Diango to celebrate the royal wedding between the King Black Dragon and the Kalphite Queen (and the real life marriage between Kate Middleton and Prince William which it parodies). When thrown, it leaves a small smoke cloud which lasts for a few seconds before completely disappearing.
Firecrackers are currently the only celebratory/wedding items that can be stacked.
Throwing firecrackers uses the same animation as using Calling beads.
When throwing firecrackers against something you can not walk on, like water, the firecracker will not explode one space ahead of you like it will usually do, but instead blow up on the square your character is standing on.
If you try to throw a firecracker inside a bank and some buildings it will say, "You can't throw firecrackers here." This also includes 1 square away from the Grand Exchange tiles.