Can I choose or change my IP address on Firefox Private Network?

No, the IP address is set by Firefox Private Network and cannot be changed or chosen.

Firefox Private Network is an extension which provides a secure, encrypted tunnel to the web to protect your connection and your personal information anywhere you use Firefox. Whenever you are on the move, you may find yourself taking advantage of the free WiFi at the airport or a cafe. Did you know that there are other people using that same network? This leaves your personal information vulnerable. By using the Firefox Private Network it keeps you protected from hackers lurking in plain sight on public connections. To learn more, see Firefox Private Network extension - browse securely on public Wi-Fi.