For some reason you might not want to flash the global ftf or ftf from any other region.
For guys like me who wanted to flash 4.3 using the original customization number of their phone (which means got updated using PC companion with LOCKED bootloader OR used the ftf with their ORIGINAL customization number), Please point this out:
You need to extract the kernel from the 4.3 firmware that you USED to update.
If you updated with the PC companion but instead used the .266 stock kernel from the [UNLOCKED BOOTLOADER SECTION], chances are your device will not boot up and (if you are a noob like me) you'll start to panic like HELL.
- Create your own FTF from Sony Update (SUS) / PC companion. GUIDE
- Extract the kernel (kernel.sin) from your 4.3 firmware ftf. GUIDE
- Convert kernel.sin to kernel.elf GUIDE ***My flashtool is v0.9.11.0 - use the guide until step 2. The flashtool menu will be different so in flashtool, go to: TOOLS>SIN EDITOR, then browse for the kernel.sin you just extracted. then click EXTRACT DATA. You have now the kernel.elf in the same directory as the kernel.sin. You can use the kernel.elf to flash with the use of QuikIMG tool to flash your own stock kernel.
ALSO, please include a remark that for people who have 4.1.2 LOCKED BL, with ROOT, it is safe to UNLOCK YOUR BOOTLOADER as long as you back up your TA partition. You can restore the backed up TA from 4.1.2 when you have 4.3 to RELOCK your bootloader. It's MUCH MUCH EASIER this way.