From the moment you apply power, your controller is always fanatically busy fetching instructions and executing them, wheter you provide a ROM or not (until you put it in IDLE or POWER DOWN mode or switch the power off). If you have the /EA line low, it will still insist on fetching instructions from the external ROM chip, no matter what. Only YOU know there IS NO ROM chip. The controller isn't aware of this, it is a dumb piece of silicon. So it will attempt reads, but the "instructions" it reads back will be whatever the floating P0 will happen to pick up from thin air. Maybe it's something which reads as MOVX, who knows. Whatever you are seeing, it is not the result of a deliberate program anywhere.

'Micro code' is not a program, but on CISC chips (as opposed to the more recent RISC chips, and the 8052 IS a CISC chip) the microcode is a table of steps the controller needs to take on the lowest hardware level to execute each instruction of the instruction set as you know and use it. Essentially, the CPU fetches an instruction, and then translates it into smaller steps according to the microcode ROM. These steps include those responsible for sending the PC to an incrementor, putting the output of tha ALU on the internal data bus, etc.