my version 151.0.2 (64-bit) must support built-in VPN but the VPN setup prompt is not found in the top-right corner of Firefox toolbar nor the VPN icon is found in the toolbar.

Hi,

The Firefox built-in VPN is being introduced gradually. It’s available to some users in the US, UK, Germany, France, and Canada.

If you’re in one of these countries, but still don’t see the built-in VPN, it may simply not have reached you yet. Since this is an experiment, the feature is being rolled out in stages.

Hello

To complement

This discussion thread https://support.mozilla.org/en-US/questions/1584321