When I install Firefox for the first time I can get Firefox own VPN for free but soon as I sign in it goes away

Looks like you are using an Android Mobile, there is a forum for that https://support.mozilla.org/en-US/questions/mobile

https://support.mozilla.org/en-US/kb/built-in-vpn https://support.mozilla.org/en-US/kb/unable-find-built-vpn-firefox However if this is about the built-in VPN in Firefox for Android then I am not sure about the current status of the experimental rollout since July 14 as the KB article https://support.mozilla.org/en-US/kb/mobile-android-vpn was made restricted last week.