Heimdall error libusb error: -12
Inside Heimdall zip there is a driver folder. 


Run the zadig.exe
click options - List All Devices
Choose your phone from the drop down list (on my pc it was "MSM8960"


I could not get it to work correctly on my PC, onece plugged into laptop "SAMSUNG Mobile USB CDC Composite Device")

Go through the drivers (WinUSB, Libusb0, Libusbk) and clikc Place drive for each of them.
Then run Heimdall


This worked for me but I had to do it on my laptop to be able to flash the files correctly.

I still get problem installing with my phone having an issue with the downloading bar going all across the screen and then stopping the flash.

to get around this I did one file at a time and allowed it to auto reboot. Each time putting it straight into download mode.

Source: http://redialflash.blogspot.co.uk/2013/05/how-to-install-and-succesful-start.html