firstly

副词 firstly:

1. before anything else
   同义词：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.
   如果我们要跳舞的话，你们可以帮我准备一下。让我们先把房子中间的东西推到一边去。
2. The illness can develop in two ways: firstly, in cases of high blood pressure and secondly ...
   这种病有两种情况: 第一，由高血压引起; 第二 ...

first.ly

adv.（副词）
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:
有许多规范的先例同时使用first 和 firstly 来开始列举：
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.
不管选用了哪个词，如果后面还有并列列举的条目，要符合一致性原则，例如 first…second…third 或者用 firstly…secondly…thirdly