FIREBinaryPath is an option for FIRERunReduction. It specifies the full path to the C++ FIRE binary.
FIREBinaryPath
FIRERunReduction
The default value is FileNameJoin[{$UserBaseDirectory, "Applications", "FIRE6", "bin", "FIRE6"}].
FileNameJoin[{$UserBaseDirectory, "Applications", "FIRE6", "bin", "FIRE6"}]
Overview, FIRERunReduction.