I’m not very experienced with X-windows on the Linux platform, so I’m not too skilled in troubleshooting issues with the display. I recently upgraded an Ubuntu system at work to use Ubuntu 9.04 (Jaunty Jackalope), which only has Firefox 3 available (no package for Firefox 2). I had a Selenium server setup running tests, but they stopped working after I upgraded to this newer version of Ubuntu.

I thought that perhaps Selenium wasn’t compatible with version 3 of Firefox, but this isn’t the case. The Selenium website says ‘Firefox 2+’ for browsers running on Linux.

The error I was receiving when I would run a test was:

10:46:19.778 INFO - Preparing Firefox profile...
Error: no display specified

After a bunch of research and Googling online, it turned out I just needed to run this before I started my Selenium server:

export DISPLAY=:0

I hope this saves someone else some time.