*** 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 M (C1905)
Firmware version: 15.4.A.1.9_R3C
Region: UK (Generic) [1274-5523]
Android version: 4.3

Xperia M_C1905_15.4.A.1.9_UK_Generic 4.3
Sony Xperia M (C1905) Android 4.3 firmware - Generic UK