All you have to do to back up Thunderbird is periodically copy the entire Thunderbird folder to another location. I use an automated program to back it up every few days, but you can do it manually as needed.
The Thunderbird folder is at: C users yourusername appdata roaming and is visible only if you view hidden files in Explorer. It contains your email, addresses, and configuration. The Thunderbird installation at C Program Files is the program itself, but not your personal Thunderbird profile, email, addresses, etc.
If you ever reinstall Thunderbird, you can copy this backed up folder over the newly created version and Thunderbird will be ready to go, with your old email, addresses, and configuration in place.