This FiR derailleur was part of a mountain bike groupset that came in boxes carrying the words 'La Nuova Dimensione' (The New Dimension). For this reason the derailleur is often called the 'FiR La Nuova Dimensione'. But I think that 'La Nuova Dimensione' was more of a strapline and less of a model name. I have also been told that this fine mech was called the 'FiR Nettuno'. This sounds more plausible as Nettuno was a name that Fir used for a mountain bike rim. It seems convincingly consistent with the road derailleurs which also had classical names, Gemini and Apollo. All that is lacking is any real evidence.
This derailleur was manufactured by DNP of Taiwan. DNP marketed this model as the DNP Epoch 1. However the FiR version was markedly more attractively detailed, markedly better finished and markedly more expensive. It was one of the very first Taiwanese-made derailleurs to sell on quality rather than low-price.