I already pay for Mozilla's VPN - why a FireFox VPN ? Too ?

There is no "Firefox VPN" though there is a built-in VPN in desktop Firefox and perhaps soon in Firefox for Android. https://support.mozilla.org/en-US/kb/built-in-vpn The built-in VPN has more limited features and only a 50GB data limit each month. Also the built-in VPN feature in Firefox operates via a secure proxy network rather than a traditional, full-device virtual private network like the standalone Mozilla VPN app. https://www.firefox.com/en-US/features/browser-with-built-in-vpn-secure-browsing/