Yes.
Actually, I just found a solution. Firefly was not correctly installed due to some little endian / big endian problem.
All the trick with a valid package is exposed here:
http://www.synology.com/enu/forum/viewtopic.php?f=55&t=5240&st=0&sk=t&sd=a
Hope this may help other people.
Thanks for your time Marting.