If you're using JFW DH 3.56 MA, you would know that one of the limitations is that you're basically stuck on that firmware. This was due to Sony introducing a new 'updater2' which does not recognize any of the firmware updates that use the previous 'updater1'. To combat this, Universal MAD Downgrade has been put together to allow users to downgrade their PS3s to 3.51 or 3.55. Here's a rough translation provided by hellsing9 of PS3Hax.
You can lower from any version from jfwdh356 the times you want, this way many users that were not willing to test it (for x reasons) Now will can try and see the great capacity and work been done in this jfw356.
Also Demon and Kike said to me that you will can downgrade to 3.55 or 3.51 (clean)
Allowing you to install any CFW or JFWDH3556.
This is what many people were waiting for, well soon will be available in his web and here.
Needless to say this year will be full of surprises regarding JFWDH356 and who knows maybe they can achieve an JFWDH3.60 or JFWDH4.11.
Source: Zrandiscene via PS3Hax