Yesterday, i posted the PS3 firmware update news here:PS3 New system firmware V4.00 is coming
Here is an update news from the E3 flasher official site
E3 flasher downgrade OFW4.0 to 3.55 successfully, it's same way as downgrade 3.73 to 3.55.
We suggest user upgrade to OFW4.0 and then downgrade to 3.55 from now on. And don't forget backup your OFW4.0 bios well .