*** 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 SP (C5306)
Firmware version: 12.1.A.1.205_R3B
Region: US (Generic) [1272-4529]
Android version: 4.3

Xperia SP_C5306_12.1.A.1.205_US_Generic 4.3
Sony Xperia SP (C5306) Android 4.3 firmware - Generic US