*** 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 Ultra (C6806)
Firmware version: 14.6.A.1.236_R2D
Region: US (Generic) [1276-1569]
Android version: 5.1.1

Xperia Z Ultra_C6806_14.6.A.1.236_US_Generic 5.1.1
Sony Xperia Z Ultra (C6806) Android 5.1.1 firmware - Generic US