Make sure you have the shares directory in your unslung config file set for sharing … the default IP to THIS config file is 192.168.1.77. You find this configuration item under Administration > Advanced > Shares. Click on the share and then click the “Access” button. It should appear in the “Groups with Access” box on the left; if not, highlight it and click the arrow key for “R/W Access” to move it to the left box. Save the config and exit out. I reboot the slug after doing this, although I’m not sure that’s entirely necessary.
Then you should be able to use the Firefly config file at 192.168.1.77:3689 (that’s the default IP address).