I believe I've managed to shed some light on the confusion of the dates surrounding 'Firefly'. In the 1936 'Herald' newspaper article Mr. Rossi himself explains that he had been trying to obtain a fixed sport for "more than 20 years". The streaked sport didn't often come true and he said it was only "a couple of years ago the variety was fixed". He exhibited 'Firefly' for the first time in 1936. He mentions that he did not intend to commercialise it in Australia until deals were finalised in the US.
So it would seem to me that 1912 is the likely date of the first appearance of the sport on 'Rosomane Narcisse Thomas', but 1933 seems to be about when he successfully fixed the sport. Perhaps it was never properly introduced in Australia. I've checked the online records of the Hill Floral Co, but they only go up until the early 1930s, so I can't shed any light on its appearance in America.

Also, I seem to remember seeing a photo of this rose years ago in perhaps one of the heritage rose journals. If I remember correctly it was a bit thin and shaggy. I don't know if anyone might be able to find this and possibly upload a photo.

Edited to add: There are in fact newspaper articles from 1933 when he exhibited 'Firefly' for the first time at the Malvern Rose Show. I'll add these references soon.