title: Xvfb & Docker - cannot open display
body: <p>I need to run XVFB and docker with firefox but can't get them to work together</p>
  
  <p>Here is my Dockerfile :</p>
  
  <pre><code>FROM abevoelker/ruby:latest # based on ubuntu
  ENV TERM linux
  RUN apt-get update &amp;&amp; apt-get install -y .....
  
  ENV DISPLAY :99
  
  # Install Xvfb init script
  ADD xvfb_init /etc/init.d/xvfb # default xvfb init.d
  RUN chmod a+x /etc/init.d/xvfb
  
  CMD ["firefox"]
  </code></pre>
  
  <p>The error message I get from Firefox is</p>
  
  <pre><code> Error: cannot open display: :99
  </code></pre>