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Apparently, Europe was exposed to gunpowder prior to Marco Polo: the Wikipedia page references several sources speaking of Mongol usage of gunpowder at the Battle of Mohi (Hungary) in 1241; Marco Polo was not even born at that time.
This page ends with the following rather assertive sentence:
There is, however, no truth in the tradition that he brought back the secrets of gunpowder, the compass, printing or noodles.
Apparently, gunpowder and firecrackers were described in 1267 by Roger Bacon (Marco Polo was 13 at that time, and had not yet departed to, let alone returned from, China). Firecrackers and fireworks are not exactly the same thing, although they are both used for festive and ritual reasons. Fireworks properly said (i.e. the ones which go up and are meant visual rather than auditive usages) were common in Song's China, especially during imperial celebrations. Since the Mongols (Yuan) adopted the pomp of the Chinese court, it is highly probable that Marco Polo, during his 18 years presence at Khubilai's court (1274 to 1292), saw quite a lot of it.
It is hard to prove a negative, but chances are that Marco Polo bringing back gunpowder or any derivative (e.g. fireworks) to Europe is a myth. As all popular myths, it also includes variants; e.g. that page depicts Marco Polo bringing gunpowder to the Chinese, not the other way round.