I managed to finally update the firmware from a non-stock JF3 rooted firmware, on a German phone with UK firmware, in South Africa!!!

I tried all kinds of things and could not get KIES to update to the new firmware, no matter what firmware etc I used. Here is what finally worked for me :

- Flash with JF3 from Samsung-firmwares if you are not running this already, does not matter if rooted.
- Start KIES without connecting the phone, open firmware upgrade and hold keys ctrl+alt+u+p to get it to go into test mode
- Connect the phone and viola, you can upgrade!

Note, this does not seem to work on the newest KIES version. I tried this on both my netbook (old KIES) and my pc (newest KIES) and only the old version worked. I am ugrading as I type.

Note this may not work on branded phones. I own an unlocked SGS