My PS3 is a UK-purchased 2503A with factory installed firmware of 3.50. So while it's not certain, it at least seems very likely that your friend's same model is also CFW compatible.
@DeViL303
Thank you I know it. Thats why I wrote this because years ago in flashers ages there were 2 column in 25xx slims:
1. jailbrakeable and downgradable to 3.55 using 9.99 downgraders or
2. JUST jailbrakeable not downgradeable to 3.55 not compatible with downgraders.
I am not sure 100% that going back to 3.55 doesnt helps anything anymore..but you are the expert.
[@Coldheart2236
Both 3.55 & 3.56 minVer were/are CFW compatible]