Please Help me with my script

i want to make the script automatically click the open firefox window and click a certain form box and enter numbers 001 to 999 in order and hit enter after each number is entered this is as far as i got.
there must be a better way


MouseClick("left",748,4,1)
MouseClick("left",598,583,1)
Send("{BACKSPACE}{BACKSPACE}{BACKSPACE}001{ENTER}")
sleep(20)
MouseClick("left",748,4,1)
MouseClick("left",598,583,1)
Send("{BACKSPACE}{BACKSPACE}{BACKSPACE}002{ENTER}")