it will work on a slim but it wont work on every slim it dont matter what FW its on
on the back of the ps3 on the sticker where the serial number is itll end in
cechxxxx
xxxx can be cech 3000 cech 2501 and so on cech3000 and cech4000 models can not be downgraded which is due to the new mtldr2 which is
down the console needs to be downgraded for this to work
cech2501 and below can be downgraded but on cech2501 you need to check the min firmware it can be downgraded to because some of these have pre installed 3.56 ofw along with mtldr2
ps3's can be downgraded as far as first ofw that were released
long as it can be downgraded to the min of 3.55 ofw you can test this
theo can you post the cech model?