Hello,

I have exactly the same problem but I do not use Norton (Bitdefender instead). After restarting my PC FD has vanished.

I move to AddOns and "Find Updates" .

After restarting FF (V3.6.2) FD is available again.

After reboot the cycle starts again.

I had no problems with FF 3.5.x or any other AddOn.
Help appreciated.

Greetings R_P