Hi Rob1949Scott, Welcome to LQ. Try the following, taken from the Linpus website to access a terminal.
The Steps to open a terminal window:
1. Press "ALT + F2"
2. Enter "terminal"
3. Enter "su -"
4. Enter your root password
Once you have this access you'll want to navigate to your user home directory, locate the .mozilla directory and rename it .mozillaold. Exit from the terminal and see if Firefox will start up for you after that.
Good luck. ;-)