A printer includes a printer having a pagewidth inkjet printhead. Feedback lines from the printhead are coupled to a processor that controls the printhead. Signals conveyed on the feedback lines indicate parameters such as the temperature of the printhead, available printhead actuator voltage, actuator heater resistivity and actuator heater width. A firing pulse circuit processes the temperature and voltage signals on the feedback lines to generate firing pulses that are applied to the printhead. The firing pulse circuit includes sample and hold circuits and analog to digital converters that convert the temperature and voltage parameters to digital signals that are applied to a memory table. The memory table is loaded with values by the processor. The processor determines the memory table values on the basis of a user brightness setting, an ink viscosity curve, actuator heater resistivity, the actuator heater width and the voltage and resistivity signals. Consequently a pagewidth inkjet printer is provided with firing pulses that are dynamically adjusted according to the printhead's operating conditions.