How do I use OpenVPN for only one window/process?
Example Case Scenario:
I want to use a US only website on Firefox, but use my ip on the chromium process
The only way you could do that would be to have a proxy server on the same network (or host) as the OpenVPN server and to configure Firefox to use that proxy. You'll have to ensure that the OpenVPN server only pushes routes to it's own network and doesn't make the VPN the default route.
This is because OpenVPN (and indeed any true VPN) works at a networking level, not a process level.
At a high level, configure: