in case you're still curious, this might be why it worked:

mount /dev/sda1 /mnt/fw

is different from just

mount /dev/sda1

or

mount /mnt/fw

if you give mount just one argument, it looks for that mountpoint in fstab to figure out what device to attach at that mountpoint. giving it 2 args tells it what device to mount explicitly. anyway, that's why it works once you put in the line in fstab.

--ben