Forget about using Gnome to do this. Use the command line instead.
First verify that Linux is seeing it properly. Try something like this:
right after you hook up the firewire device. You should get some clue as to how Linux is seeing the device. It should be seen as "/dev/sdb2" or something like that. After you've determined the special device file for the drive you need to create a mount point and then mount it. This is not very hard to do.
A mount point is just a directory so create a new directory:
sudo mkdir /some_mount_point
Now you need to mount the partition to the mount point:
sudo mount /dev/sdb2 /some_mount_point
The mount command will only be successful if Linux can tell what type of file system is on the partition. If it can't then you might have to specify it (but you probably won't have to do this).
At this point the partition will be mounted and a window will probably pop up on the screen. Irregardless, you can see what's in the directory like this: