before anything else
"first we must consider the garter snake"
In the first place; before anything else; first.
"Firstly, we need to ensure that everyone is present before beginning the meeting."
In plain English: Firstly means you are starting to list things by saying it is number one.
"Firstly, please fill out your registration form before we begin."
Usage: Avoid using "firstly" in lists, as modern style guides prefer the simpler "first." It often sounds awkward or overly formal compared to alternatives like "to begin with."
Firstly was coined before 1475 by combining the word first with the suffix -ly. It entered English as a straightforward formation meaning "in the first place."