Docs say: Xvfb runs on port 99, and the appropriate DISPLAY environment variable has already been set. ' Error: no DISPLAY environment variable specified. Setup GeckoDriver using System Properties in Environment Variables.
A display consists (simplified) of: a keyboard, a mouse. I think with Leopard, Mac OS X always provided a DISPLAY environment variable, and if something used DISPLAY's contents, X11 would be automatically be started. In the Tasks tab of the release pipeline, choose the + icon in the Run on agent section.
What struck me was that it wasn't using -headless as an argument to Firefox, which would explain why it would complain about the DISPLAY env. No display environment variable specified selenium 3.
