*** YOU NEED TO REGISTER ON THE FORUM BEFORE YOU CAN ACCESS THE DOWNLOAD LINK ***
INSTALLATION INSTRUCTIONS
http://www.xperiablog.net/2015/03/17/guide-to-installing-xperia-lollipop-using-xperifirm-and-flashtool/
- Open link above and skip to the section entitled “FlashTool steps”.
- As you have already downloaded the FTF firmware file, skip to the section where you need to “Flash device”.
XPERIA FIRMWARE DETAILS
This is official stock Sony Xperia firmware.
Model: Sony Xperia Z (C6606)
Firmware version: 10.4.C.0.814_R12C
Region: US (T-Mobile) [1272-8668]
Android version: 4.3

Xperia Z_C6606_10.4.C.0.814_US_T-Mobile 4.3
Sony Xperia Z (C6606) Android 4.3 firmware - T-Mobile US