Both expressions are used to order the points you are making. They're basically interchangeable in meaning. First off is rather informal. We often use is for emphasis or when we're correcting people's accusations or when we're irritated. First off, I didn't call your boyfriend. He called me! Second of all, you guys broke up four months ago! I'd like to know, first of all, where you've been. First of all, I don't own you an explanation.

yo creo que más bien se refieren a "first of all", lo que significa "primero que nada"