I wouldn't trust eyewitness` reports about engine fire. Sometimes they report about UFO...
It could be pumpage caused by high AOA during stall.
A message of the russian aviation authorities has been published today. It describes all technical and weather detailes but the most interesting and important is the fact that autothrust had been disabled on this plane on Sept 12th, one day before it crashed.
This failure is described in MEL and it's allowed to fly without AT but the authorities prohibited it until further instructions.
Don't want to make any conclusions but it gives some information to think about...