Fujifilm just released the new Firmware for all X-series cameras and for the XF50-140. This firmware adds XF35mmF2 and 1.4x Teleconverter support. X-A1, X-M1 and X-E1 also get Windows 10 support. All download options here. Download the Fuji X-T1 Firmware ver. 4.10 here.
When updateing the XF50-140 FW here, upgrade the firmware of a camera to the latest version first and then upgrade the firmware of your lens.