This is the ugly type of a regular kernel panic. "firefox" and "panic" are two different lines. One could read it as "firefox panic", though :-) But it isn't, it's the system that crashed, not Firefox/TenFourFox.
First please perform the Apple Hardware Test that came on the original install DVD/CD for this Mac. Make sure the HD test and the extended RAM test pass. (Kernel panics are usually due to a failing HD or defective RAM).
If everything is o.k., open Disk Utility and check the SMART status of the startup disk. The click "Verify Disk" and let it repair any errors.
The third common reason for panics are third-party Kernel Extensions, did you install anything recently?