capybara, webdriver not launching on xvfb display

Hey Guys,

I'm trying to run cucumber (capybara) in a xvfb, I've set it up correctly, and can manually launch firefox using "DISPLAY=:99 firefox". I'm 100% this works, because I've set up a vncserver bound to that xvfb, and I can see firefox comes up..

But if I DISPLAY=:99 cucumber, firefox doesn't bind to that display and times out after 60 seconds. Any ideas on what could be causing this and how I can resolve?

I've even tried to launch xterm into the xvfb and run cucumber in there, with no luck. DISPLAY=:99 rake cucumber:all doesn't seem to work either. I'm thinking this has something to do with the way webdriver launches a firefox instance. I can't seem attach it!

Any help would be appreciated.

Many thanks, Mark