To mount an external firewire HFS+ formatted Mac drive in Linux -

First, connect the drive.

Then, see what the computer named it

dmesg | tail

You will see something like

sd 9:0:0:0: [sdb] Attached SCSI disk

Then, make a mount point (any directory, but customarily in /media)

sudo mkdir /media/macdrive

Then, mount the drive to that folder (assuming HFS+)

sudo mount -t hfsplus /dev/sdb /media/macdrive/