How to put macbook pro in disk mode

Is there anyway i can put my macbook in disk mode and use it as a passthrough to transfer files off a hard drive that only has a firewire port to a usb 3 hard drive.
The reason I'm asking is the first hard drive is from an audio recorder and I'm not sure if it will be recognized as a readable disk

Target disk mode isn't going to quite do things that way. In order to pass things from the first hard drive to another one the Mac will have to be able to "see" the drive. It doesn't function as a passthru.

What format is the disk that you are trying to read in. If it is FAT 32 or NTFS the Mac will read it with no trouble. If it is a format that the Mac cannot read you should see a message that the disk is not readable. Then you will be asked whether you want to format/initialize it. Choose Cancel and your data will be unharmed.