PKM, I'm sure one of our 777 drivers out there can give you chapter and verse, but our in house magazine published pics of a broken HP turbine blade which caused the whole problem. The engine obviously then went out of balance, giving a vibration warning (not fire warning) on the flight deck. The crew throttled the engine back as required by the checklist but then became aware of the smoke, hence the hasty return.
The smoke was caused by engine oil being released into the conditioning ducts by damaged oil seals.