firmware/third_party/mla_v2013_12_20/apps/usb/device/bootloaders/ : Original Microchip version
firmware/third_party/mla_v2013_12_20/apps/usb/device/bootloaders/firmware/pic18_non_j/ : Customize to Esrille New Keyboard

Note the bootloader memory boundary has been moved to 0x1800 for using the XC8 compiler in free mode.
firmware/third_party/mla_v2013_12_20/apps/usb/device/hid_keyboard/firmware/ : Customize for the updated HID boot loader