Which German city suffered the worst firebombing during the WW2?

The bombing of Dresden was a British/American aerial bombing attack on the city of Dresden. In four raids between 13 and 15 February 1945, 722 heavy bombers of the British and 527 of the United States dropped more than 3,900 tons of high-explosive bombs and incendiary devices on the city. The bombing and the resulting firestorm destroyed over 1,600 acres of the city centre. An estimated 22,700 to 25,000 people were killed, although larger casualty figures have been claimed over the years.