In addition to "Only VPN" and "Bypass VPN", I want to be able to set some applications to "VPN If Available".

I want to be able to set "All Other Apps" to "Bypass VPN".

I then want my browser (Firefox), and some other apps, to use VPN if it's available (connected), else, revert just to my normal internet connection.

As it stands, there is no option to do this. So if I could set their Network Preference to "VPN If Available" that would mean they'd use the VPN if it was connected, else revert to my standard internet connection.