I'm working on the same project using an Xubuntu base. I followed this link: http://www.instructables.com/id/Setting-Up-Ubuntu-as-a-Kiosk-Web-Appliance/?ALLSTEPS
to get the initial setup running.
Once you have the session created, you may need to edit the kiosk user's ~/.dmrc file to read:
[Desktop]
Session=kiosk
substituting "kiosk" for the browser-only session name. I also created a file in /etc/lightdm/lightdm.conf.d similar to the existing 10-xubuntu.conf specifying my kiosk session. It took all of these to get the auto-login to work properly.
Also, if using Google Chrome or Chromium check out: http://www.chromium.org/administrators/linux-quick-start to see all of the policies you can hard-configure into Chrom{e,ium}. Since I'm setting this up for a school computer lab, I found several options that will allow us to curtail certain uses.
Hope this is helpful. I am by no means an uber linux user and I managed to get it that far. Lightdm can be a bit finicky at times. Google will find some good resources but be warned that on Xubuntu 14.04 the lightdm.conf documentation lives at /usr/share/doc/lightdm/lightdm.conf.gz Several websites list other possibilities. Good luck.