Firstly I was getting the following error:
org.openqa.selenium.firefox.NotConnectedException: Unable to connect to host 127.0.0.1 on port 7055 after 45000 ms. Fi
The best approach to solve this problem is making changes to the jenkins start script.
The solution that works on Ubuntu for me correctly is as follows:
1.Open Jenkins shell script located at: /etc/init.d/jenkins.
2.Add the following lines as follows before PATH variable:
/usr/bin/X :0 vt7 -ac
export DISPLAY=:0
xhost +