I have tried pretty much every way mentioned on SO and the docs and failed.
Specifically, I'm using WebdriverJS through Node.js.
I'd want a way to programatically make Firefox-Quantum use a proxy, which requires auth and port (i.e http://user:pass@host:port).
I don't mind to use an extension for this, but I don't know which one I could use for programmatic access.
I do not want a solution involving the authentication dialog popping up and asking for the auth.
I used to manage to do it on Firefox 56.0 using an extension called CloseProxy. (As per How to set proxy authentication (user & password) using python selenium)
However, CloseProxy is not supported on Firefox-Quantum.
This is my last attempt at this issue before resorting to going ahead and writing my own Webextension for this so I hope someone somewhere has the answer