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Running Headless X Window Clients...

First start a virtual display...

  # Using Xvfb
  startx -- `which Xvfb` :1 -screen 0 1024x768x24

  # Or with Xvnc (also headless)
  startx -- `which Xvnc` :1 -geometry 1024x768x24

  # Or with Xephyr (nested X server, requires X)
  startx -- `which Xephyr` :1 -screen 1024x768x24

Now run a client (like firefox) on that display

  DISPLAY=:1 firefox

Open a web site

  DISPLAY=:1 firefox-remote http://www.google.com/

Take a screen shot

  DISPLAY=:1 import -window root googledotcom.png

Firefox has lots of javascript-magic extensions such as greasemonkey and
Selenium to let you execute browser-side javascript and activity automatically.
Combine these together with Xvfb, and you can automate lots of things behind
the scenes.

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More automated...

  ephemeral-x.sh firefox

This finds a unused display number, and runs firefox on it,
such that when firefox exits the display exits.

More complex...

  ephemeral-x.sh -x "Xephyr -ac -screen 1280x720x24" \
                 -w openbox-session firefox www.google.com

Code is in xdotool test area...
  https://github.com/jordansissel/xdotool/blob/master/t/ephemeral-x.sh

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