*** 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 ion (LT28at)
Firmware version: 6.1.C.1.111_R21G
Region: US (Generic) [1255-7823]
Android version: 4.0.4

Xperia ion_LT28at_6.1.C.1.111_US_AT&T 4.0.4
Sony Xperia ion (LT28at) Android 4.0.4 firmware - AT&T US