*** 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 Ericsson Xperia arc S (LT18i)
Firmware version: 4.1.B.0.587_R1I
Region: Nordic (Generic) [1255-1753]
Android version: 4.0.4

Xperia arc S_LT18i_4.1.B.0.587_Nordic_Generic 4.0.4
Sony Ericsson Xperia arc S (LT18i) Android 4.0.4 firmware - Generic Nordic