Firefox Live lets you open Firefox from read-only media as CD, DVD or .dmg. As Firefox doesn't support running directly from read-only media, solution (as Firefox Portable win edition) is setting the profile folder to the local user's temp directory. This folder will be deleted when user log out.
You could need a demo CD/DVD for your customer. Or use it just for privacy, but remember that profile folder till remain on temporary folder till user log out from his account, elsewhere you need to delete it manually.