Hi Danyel, We use "first of all" to describe something we must do before anything else. Example: First of all, I would like to acknowledge the kind sponsors for this event. We use "firstly" to introduce our first point or reason. Example: I have three reasons for my choice. Firstly,..... Hope this helps. Cheers, Lance

They have the same meaning, but "first of all" is much more common. It's strange because "secondly" is very common, but "firstly" sounds somewhat strange to my ears. But, if you used "firstly", people would understand what you're saying.