Xlib: extension “RANDR” missing on display…

i got in the log of my selenium based integration test against firefox inside a Xvfb server. My first thought was of a missing library but the problem is caused by selenium:

“org.openqa.selenium.firefox.NotConnectedException: Unable to connect to host on port 7055 after 45000 ms. Firefox console output:”

was the line above and i had recently updated firefox on my ubuntu 12.01 server to version 15 by normal updates. The maven dependent selenium plugin version was still the same when i got the error. After updating to the latest version everything works as before: