If iTunes is the only thing that connects to Firefly then take Firefly out of the equation.
Go into iTunes preferences and change the library location from your local hard drive to the network drive.
The files still live on the NAS but the db will be on the local HDD speeding things up considerably.
You could even symlink the iTunes music directory on your mac to the music directory on the NAS if you wanted to.
When your laptop is disconnected iTunes will complain that it can’t find the files & ask you where they are.
If you close iTunes all will work again when you reconnect to the NAS
Unfortunately, for you, I run Windoze so i can’t give you step by step instructions
This is how iTunes is set up on my PC but i rarely use it (iTunes that is). 😉