@0050 hrs The structure assignment was dispatched to 800 Euclid Ave for a report of smoke inside the bathroom. Chief 10 arrived @0052 hrs and reported a haze in the second floor bathroom and advised he was attempting to check 802 Euclid Ave for the possible source. The homeowner told Chief 10 that he had a small fire on the back porch earlier in the evening and he extinguished it with a bucket of water. Ladder 10 arrived @0056 and took the Delta side of the structure and sent its crew in to investigate. E11 & E13 arrived @0059 and assisted with interior operations. Crews found smoldering firework debris behind the siding causing smoke to enter both structures. the fire was extinguish and crews began to vent and check for extension. The fire was placed under control @0107 hrs crews began to secure all equipment and stood by while FM66 investigated the incident. All units were available at 0149 hrs.