Joe --
I know that Mint is built on Ubuntu. This post seems to suggest its been an ongoing problem:
They suggest: Make sure Firefox isn't running. Then rename ~/.mozilla to something else and see if Firefox still crashes.
I would suggest searching for the FF error logs. This post tries to shine some light on their location:
I would spin up a VM and see if you can duplicate the issue in a Vanilla version of your OS ... straight outta the box, does it happen?
Try to reign in the scope of the issue with VM troubleshooting.
Let me know if that helps at all! :D
-Alex.