We don't advice to downgrade and we don't promise that the TV will work after this procedure.
Just using an older version and be happy with it, is not possible as there are components in the TV depending on the Firmware and a certain version.
By downgrading without professional help one can possibly damaged your TV.
Worst thing of all is that by doing that you loose warranty.
Just to make that clear, advises from users to downgrade are their personal advises, not official Philips instructions.
You do that at your own Risk!