Over a month ago papa44 made mention HERE that he was planning to share PS3 Debug Firmware Update 2.52 with our community. Sadly, after stating he was uploading it he never replied again... and to date has been online only lurking.
Just recently I ran across it myself, but since it didn't come with any documentation all I had was a PS3UPDAT.PUP file that WinHex showed as being "2.52" (122 MB - 128,615,182 bytes).
The good news is, CJPC was able to successfully install and confirm for us that it is indeed a legitimate PS3 2.52 Debug Firmware update file, and as a result we have now added it to our PS3 Debug Firmware section for those interested!
Some changes CJPC noticed during his brief time testing it out were as follows: It now includes Network emulation and you can now save the PUP files on the PS3 HDD and access them later.
For example, if you click System Update, then Install from HDD, it will give you a list of PUPs stored on the HDD which can be installed. Additionally, all of the PS3 2.52 dev_flash files (even the hidden ones) such as the SPRX's, etc are dumpable again... needless to say they are all encrypted.
However, these in particular are interesting as they hint of PS2 emulation coming:
Finally, those with Retail PS3 consoles with Firmware higher than the last (public) 2.30 Debug Firmware (but still under 2.52) can now update to the 2.52 Debug Firmware to check out the non-functional menu options if desired, and then update to Retail 2.60 PS3 Firmware when you get bored or wish to play Blu-ray movies again.