副詞 firstly:

1. before anything else
   同義詞：first, foremost, first of all, first off

1. If we are going to dance, some of you can give me a hand to clear the decks. Let's firstly shove the things out of the centre of the room.
   如果我們要跳舞的話，你們可以幫我準備一下。讓我們先把房子中間的東西推到一邊去。
2. The illness can develop in two ways: firstly, in cases of high blood pressure and secondly ...
   這種病有兩種情況: 第一，由高血壓引起; 第二 ...

first.ly

adv.（副詞）
In the first place; to begin with.
第一；首先

There is ample reputable precedent for using bothfirst and firstly to begin an enumeration:
有許多規(guī)范的先例同時使用first 和 firstly 來開始列舉：
例句：
Our objectives are, first (or firstly ), to recover from last year`s slump.
Our 0bjectives are， first（或 firstly ）， to recover from last year`s slump

Whichever is chosen, however, consistency is best served if any succeeding items are introduced by a parallel form,as in first . . . second . . . third or firstly . . . secondly . . . thirdly.
不管選用了哪個詞，如果后面還有并列列舉的條目，要符合一致性原則，例如 first…second…third 或者用 firstly…secondly…thirdly