Did a search on the Frigidaire site and here could find no info using the given Model Number. Then tried FGFL79 and all that comes up are stoves.
Cannot fault your logic in replacing the heating coil, I would have done the same thing. This one is going to be a pain.
I would try to get my hands on a clamp on current meter so you can monitor the amperage the unit is pulling. This will tell you if something is shorting or if the unit is pulling current that is too close to the breakers trip point.
Only other thing I can think of is perhaps one of the thermostats is opening and shorting to ground.
Try different temp settings and see if it trips ealier on higher temps.
You will have to let the unit cool down between tests for this to be valid.
I assume you have tried different timer cycles and times to rule out a timer issue.