https://www.whonix.org/wiki/Template:FoxyProxy no longer works for me with Tor Browser 7.0a1-hardened (based on Mozilla Firefox 45.7.0). Can you check please? @HulaHoop
What about installing foxyproxy using Tor Browser add-on manager rather than from Debian repository?
This also needs testing in combination with GitHub - Kicksecure/apparmor-profile-torbrowser: AppArmor profile for The Tor Browser Bundle (TBB) - https://www.whonix.org/wiki/AppArmor - for better security (hardening).. Recent fix. Can you install apparmor-profile-torbrowser from source please? (Or manually active the updated profile.)