Imports company Fast Line Imports Ltd, which is based in Cheshire, was fined almost £40,000 after being prosecuted by North Yorkshire County Council's trading standards team
Trading standards officers said the 'throwdown' type fireworks, more commonly known as Fun Snaps, contained an "unknown explosive ingredient" that was not the one listed on the label and also exceeded noise limits.
This meant the fireworks were incorrectly labelled with a CE mark, which is used to confirm that goods comply with safety regulations.
Fast Line Imports Ltd pleaded guilty to three offences under the Pyrotechnic Articles (Safety) Regulations 2015 in a hearing at York Magistrates' Court.
It was fined £39,000 and ordered to pay costs of £2,245.
Trading standards officers issued a suspension notice preventing the product from being sold or supplied but the company failed to tell officers which wholesalers it had previously distributed the product to, meaning a complete withdrawal from sale could not happen.
Magistrates who heard the case said: "It beggars belief that you failed to co-operate with trading standards."
They also considered that the product "presented a significant risk".
North Yorkshire County Council's executive member for trading standards, Cllr Derek Bastiman, said: "A business that imports fireworks into the UK bears responsibility for ensuring that they are safe and meet safety and labelling standards.
"This company did not complete the appropriate steps to check the throwdowns were safe and then failed to assist the council's officers in removing the product from the market.
"This is disappointing and irresponsible and the court recognised that in the sentence it passed."