firstly . . .

I am a native English speaker; my profession is English-language editing. I work with many scientists. A lot of these people insist on starting sentences with "Firstly . . . " and "Secondly . . ." etc. These are not native English speakers.
I always change it to "First" "Second" etc., because to me, adding the "ly" makes it an adverb, which makes no sense at all.
Does anyone know what is correct? Is this perhaps a British-English way of speaking/writing?
Thanks!
susan

Welcome .
You raised very important question .
I haven`t listen ( Firstly ) yet !
I really hope any one tell us .

First of all .. this we may used in written or speaking . But , I don`t know about ( Firstly ) .

I don't know the answer (I personally use "first of all" or "first off"), so I did an internet search and came up with:
The Mavens' Word of the Day
and:
"Bob Dotson, of West Bloomfield, Mich., writes: “It seems to me that lots of people overuse certain words that end in ‘-ly,’ but I’m not sure I know all the rules. I know better than to say ‘I feel badly,’ and when trying to emphasize a point, I think it’s correct to say ‘more important,’ rather than importantly’ -- but I’m not sure why that’s the case. I also believe that when listing related thoughts, standard English calls for ‘first,’ ‘second’ and ‘third,’ rather than ‘first,’ ‘secondly’ and ‘thirdly.’”
Dear Bob: The rules (or, really, advice) about “-ly” words can be really confusing, but let’s give it a try. The reason “I feel bad” is considered good English, and “I feel badly” less good, is that in this sentence “feel” is serving as a linking verb. “Be” is our most common linking verb, and unlike “feel,” it’s hardly ever anything else -- so if we consider how forms of “to be” work in sentences, we can see what’s going on with “feel.” We wouldn’t say “My health is badly today.” “Is” links the subject “health” to the adjective “bad,” and “bad” modifies “health.” Similarly, in “I feel bad,” “feel” links “I” to the adjective “bad.” It’s not that I’m doing my feeling in a bad manner, or “badly,” but that how I feel -- the feeling I’m experiencing -- is “bad.”
As for “more important” in sentences like “More important, others may feel bad too,” the traditional view is that it’s a shortened version of “what is more important.” Hence the lack of “-ly.” Some authorities are in favor of “more importantly,” I have to admit. They argue that there’s not much logic behind the “more important” tradition, and that “more importantly” is like other “-ly” words that often begin sentences, such as “consequently,” “oddly” and “obviously.” But traditions don’t have to make sense. I stick with “more important.”
“First,” “second” and “third” at the beginnings of sentences are traditional too. People have been using these words in this way for about 600 years. “Firstly” has almost as long a history, but “first” has two advantages: It’s a syllable shorter, and it sounds less pompous than “firstly.” "
Hope that helps!
(And I never noticed what a weird word "first" is. First. First. First. O_o )

from AHD:

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.

Hi,
First and firstly are both correct according to the Oxford Dictionary, they are used to introduce a series of facts, reason......
Firstly is more common in British English than Am. Eng.

The function is just like abverbs below:-

Subsequently,........

Eventually.........

Finally....

bye

Y'all don't need my help here.

;-)