Which broom company makes the Firebolt?
THE FIREBOLT: This state-of-the-art racing broom sports a streamlined, superfine handle of ash, treated with a diamond-hard polish and hand-numbered with its own registration number. Each individually selected birch twig in the broomtail has been honed to aerodynamic perfection, giving the Firebolt unsurpassable balance and pinpoint precision. The Firebolt has an acceleration of 0–150 miles an hour in ten seconds and incorporates an unbreakable braking charm. Price on request.
Prisoner of Azkaban - page 43 - Bloomsbury - chapter 4, The Leaky Cauldron
According to Quidditch Through the Ages, the Nimbus Racing Broom Company has been the top racing broom manufacturer basically since the company opened in 1967, but QTTA makes no mention of whether Nimbus manufactured the Firebolt.
Is the Firebolt a Nimbus broom or is it manufactured by another broom company?
★ An answer from canon, any J.K. Rowling interviews, or Pottermore would be great!