Police arrest a 21-year-old man at Sydney Airport in connection with an alleged firebombing at a mansion. Reporting across outlets says the arrest relates to an incident allegedly involving the firebombing of the founder of a popular streetwear brand. Police allege the man has some involvement in the attack, though specific details of the alleged role, motive, and how police linked him to the incident are not provided in the available summaries. The arrest occurs at the airport, suggesting authorities move to take the suspect into custody while he is travelling. The sources are consistent that the suspect is 21 years old and that the incident targets the streetwear founder at their residence. At this stage, the information is presented as allegations, and no outcome is stated regarding charges or court proceedings. The reporting also does not describe any injuries or the extent of damage from the alleged firebombing in the provided text.