I extracted it to:
C:\Users\USER\AppData\Roaming\Mozilla\Firefox\Profiles\febeprof.USER
I noticed one thing though:
On my original profile in a separate Firefox installation there was a corrupted extensions registry seemingly after the full profile+extensions backup which was done around the time of an automatic update to FF 50.0.2 (from 50.0.0). The extensions oddly did not all backup individually but the full profile backup seemed fine. I fixed the original profile which was asking to reinstall all my 30+ addons by deleting extensions.* files in the profile and manually extracting the profile data from my FEBE full profile backup (source of fix here
https://support.mozilla.org/en-US/questions/1089955).
I therefore tried another manual extraction on the target restore profile and did the same fix procedure. Positive result: session data restore is working (tabs all there), problem though is it is still asking me to reinstall all my addons even with the earlier fix pre-applied.
I will try again with a fresh backup of my original fixed profile and report back.