http://www.fujirumors.com/new-fuji-x-t1-fw-4-20-coming-on-december-17/

1. Instant AF Setting in manual focus – Focus and exposure can now be locked when the AF-L button is used in manual focus mode. You can shoot after locking AF and AE with your thumb.

2. AF+MF operation with AF-L button – The AF-L button can be used to lock focus in AF+MF mode and you can adjust the focus more accurately using the lens’s focusing ring.

3. Focus zoom in AF+MF – The FOCUS ASSIST button can be used for focus zoom and fine tuning focus using the lens’s focusing ring with focus zoom activated.

4. Flashgun in Bracketing/Continuous Shooting – Optional flashguns can now be used for bracketing and burst photography. When using the EF-X8, which is bundled with the X-T1, the flash fires in ISO, FILM SIMULATION and WHITE BALANCE BKT modes.

5. Additional Custom Display Options – Functions have been added to the DISPLAY CUSTOM SETTING option in the setup menu. Users can choose what they want, then concentrate on shooting. Additional options include: Focus frame/Shooting mode / Information background /Focus mode/Shutter Type/Continuous mode/Dual IS mode/Movie mode /Blur warning

6. Fn7 Button – The movie-record button now doubles as an Fn button (Fn7). Press and hold DISP/BACK to select what it controls.

The FUJIFILM X-T1 firmware will be available on December 17.