Thanks for everyone help.

What I did was :

LOCAL lcOldDir, lcOldPath, lcOldClassLib, lcOldProcedure, lcOldLib
lcOldDir = FULLPATH(CURDIR())
lcOldPath = SET('PATH')
lcOldClassLib = SET('CLASSLIB')
lcOldProcedure = SET('PROCEDURE')
lcOldLib = SET('LIBRARY')
SET PATH TO
SET CLASSLIB TO
SET PROCEDURE TO
SET LIBRARY TO

* call Foxfire!
SET DEFAULT TO C:\FF60
DO Foxfire WITH "REQUESTS", "", "", "FFCONFIG"

* restore environment
SET DEFAULT TO &lcOldDir
SET PATH TO &lcOldPath
SET CLASSLIB TO &lcOldClassLib
SET PROCEDURE TO &lcOldProcedure
SET LIBRARY TO &lcOldLib