Hi bahuprakash, did you get a ProtonVPN offer through Firefox? Hopefully it has a link to specific details, because I don't have that link so I can't answer this question authoritatively.

The general information on the "Plus" plan indicates 5 devices. It does not mention whether it is okay to share your login with family members. See: https://protonvpn.com/pricing

Thank you, JScher2000, Need to get in touch with Mozilla's contact for ProtonVPN.

Did you get a recent offer? I think enrollment in the initial experiment ended in 2018.

I saw it for the first time, last night.

Do you still have the URL for the offer? If it doesn't answer this question, it's probably whatever ProtonVPN's standard policy is.