I customize the pfSense sources and rename the "pfSense" to "MyFirewall" and sold it as a commercial product, I have to open my sources code or not ?
The full details are on the license page, but since the code is BSD licensed, that means you do not have to disclose the source code. You only need to keep all of the copyright notices and license disclaimers in place.
If you really want to know 100% for sure, you will need to consult with a lawyer. Which if you are seeking a commercial business, you may already have one handy.