Looking on the internet deeply has found these results:

first of all is the most popular phrase on the web.

firstly 10 results on the web	first of all 1194,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Innovative activity involves, firstly, research and development. Your fianc�e, firstly escaped from the Pescadero Mental Hospital. Gradac is firstly mentioned in 1649. branding. Europe must firstly set an example and contribute to discussions. He married firstly Isabel de Vignacourt and secondly Marie de Sennarpont. As suggested by the name, natural dyeing firstly involves making dyes from naturally occurring ingredients. This includes, firstly, genuine authorisation for multi	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

firstly

10 results on the web

first of all

1194,000,000 results on the web

More popular!

Innovative activity involves, firstly, research and development.
Your fianc�e, firstly escaped from the Pescadero Mental Hospital.
Gradac is firstly mentioned in 1649.
branding.
Europe must firstly set an example and contribute to discussions.
He married firstly Isabel de Vignacourt and secondly Marie de Sennarpont.
As suggested by the name, natural dyeing firstly involves making dyes from naturally occurring ingredients.
This includes, firstly, genuine authorisation for multi

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.