1. Verify you have given permission to the user who runs the selenium test from bash having prvilage to invoke Firefox.

2. Verify the given port is free.

3.  Stop jenkins server

4. Run jenkins from war folder  as root/administrator to get the display

java –jar Jenkins.war –argumentsRealm.passwd.user=<root user password / or a sudoer> –argumentsRealm.roles.user=<rootuser or a sudoer name>

or

Add jenkin users to access the desktop list.

(process:18728): GLib-CRITICAL **: g_slice_set_config: assertion ‘sys_page_size == 0’ failed
Error: no display specified

(process:18736): GLib-CRITICAL **: g_slice_set_config: assertion ‘sys_page_size == 0’ failed
Error: no display specified