pdf_server error Execution of Firefox to create profile failed

I've installed the pdf_server app on my server, but firefox fails to generate the PDF. I have installed all prerequisites listed in the docs.

Errors in python.log:

root@splunkpdfserver:/opt/splunk/etc# uname -a
Linux splunkpdfserver 2.6.32-21-server #32-Ubuntu SMP Fri Apr 16 09:17:34 UTC 2010 x86_64 GNU/Linux
root@splunkpdfserver:/opt/splunk/etc# tail -25 ../var/log/splunk/python.log
2010-08-04 16:15:24,053 WARNING pdfhandler:340 - body=Splunk;4.1.4;4.1.4
2010-08-04 16:15:24,053 WARNING body=Splunk;4.1.4;4.1.4
2010-08-04 16:15:24,054 WARNING pdfhandler:341 - entries=['Splunk', '4.1.4', '4.1.4']
2010-08-04 16:15:24,054 WARNING entries=['Splunk', '4.1.4', '4.1.4']
2010-08-04 16:15:24,058 INFO    xvfb:45 - Started new X server. Now 1 active
2010-08-04 16:15:24,058 INFO Started new X server. Now 1 active
2010-08-04 16:15:24,061 INFO    xvfb:205 - Assigned DISPLAY :5
2010-08-04 16:15:24,061 INFO Assigned DISPLAY :5
2010-08-04 16:15:24,061 INFO    xvfb:115 - Starting X Server: ['/usr/bin/Xvfb', ':5', '-screen', '0', '3000x768x24', '-nolisten', 'tcp']
2010-08-04 16:15:24,061 INFO Starting X Server: ['/usr/bin/Xvfb', ':5', '-screen', '0', '3000x768x24', '-nolisten', 'tcp']
2010-08-04 16:15:24,061 INFO    xvfb:116 - Starting X Server env: {'XAUTHORITY': '/opt/splunk/var/run/splunk/xvfb/xauth-5/Xauthority'}
2010-08-04 16:15:24,061 INFO Starting X Server env: {'XAUTHORITY': '/opt/splunk/var/run/splunk/xvfb/xauth-5/Xauthority'}
2010-08-04 16:15:26,064 INFO    xvfb:122 - X Started
2010-08-04 16:15:26,064 INFO X Started
2010-08-04 16:15:26,152 ERROR   pdfhandler:308 - Execution of Firefox to create profile under x86_64 failed
2010-08-04 16:15:26,152 ERROR Execution of Firefox to create profile under x86_64 failed
2010-08-04 16:15:26,174 ERROR   pdfhandler:308 - Execution of Firefox to create profile under i386 failed
2010-08-04 16:15:26,174 ERROR Execution of Firefox to create profile under i386 failed
2010-08-04 16:15:26,175 ERROR   pdfhandler:423 - Failed to start any version of Firefox
2010-08-04 16:15:26,175 ERROR Failed to start any version of Firefox
2010-08-04 16:15:26,175 ERROR   pdfhandler:637 - (500) Failed to generate a report using Firefox: Failed to start: Check that all Firefox dependencies are met
2010-08-04 16:15:26,175 ERROR (500) Failed to generate a report using Firefox: Failed to start: Check that all Firefox dependencies are met
2010-08-04 16:15:26,175 WARNING xvfb:132 - Stopping X Server 5
2010-08-04 16:15:26,175 WARNING Stopping X Server 5
2010-08-04 16:15:26,192 ERROR An error occurred while generating a PDF of this report: Failed to generate PDF: PDF server at /services/pdfserver/renderpdf returned error: Failed to generate a report using Firefox: Failed to start: Check that all Firefox dependencies are met

As per http://answers.splunk.com/questions/1218/why-does-pdf-server-fail-with-the-message-error-pdfhandler453-execution-of-fi I have tried running the binary and I am getting the result suggested by gareth's answer...but still no PDFs.

root@splunkpdfserver:/opt/splunk/etc# sudo -H -u splunk DISPLAY=none /opt/splunk/etc/apps/pdfserver/bin/firefox-x86_64/firefox
Error: cannot open display: none

Does anybody have any suggestion on how to get the pdf_server working?

[edit:] @gareth, running Ubuntu 10.04 LTS amd64. http://ubuntu.media.mit.edu/ubuntu-releases/10.04/ubuntu-10.04-server-amd64.iso. Thanks!