I have a grapefruit tree that I've had for about 25 years. I grew it from a
seed I got when I was in Florida. It is in a pot. It was left on the deck
during a frost and now all the leaves are brown and are falling off.

Is there any hope or is it a gonner - is there anything I can do to make it
recover?

I live in Pennsylvania - zone 6, I think.