There are two backup systems. Enter Backup in the search window and File History becomes available. That will only back up libraries. If you want to include any thing in user/app data/roaming (like the Thunderbird email folders) you have to put the folder into a new or existing library before it will be backed up.
The other backup system is the old Windows 7 backup which allows a disk image to be created, as well as backing up files. To get to the old backup system look to the “Windows 7 File Recovery” link in the lower left side of the File History page or search for “file recovery”.