in the first place; first: used chiefly in enumerating topics
See firstly in American Heritage Dictionary 4
adverb
In the first place; to begin with.
Usage Note: It is well established that either first or firstly can be used to begin an enumeration: Our objectives are, first (or firstly), to recover from last year's slump. Any succeeding items should be introduced by words parallel to the form that is chosen, as in first . . . second . . . third or firstly . . . secondly . . . thirdly.