From MozillaZine Knowledge Base
MozBackup is a standalone utility (for Windows only) rather than a Thunderbird extension. It works by backing up a Thunderbird profile into a single file (named "*.pcv"), which can then be restored on the same Windows computer or a different one. (MozBackup can also be used to back up and restore Firefox, Mozilla Suite, and Netscape 7 profiles.) It can be downloaded from the MozBackup homepage, where additional MozBackup documentation is also available. The download web page lists what extensions it knows how to back up/restore.
While Mozbackup is extremely popular in the forums, it's recommended that - if you plan on using it for regular backups - you first test it to verify that it will properly restore your Thunderbird profile.
Note that if extensions are included in the backup and restoration, the version of Thunderbird should be the same. For instance, if a profile (including extensions) is backed up from an installation of Thunderbird v 0.9 and restored to an installation of Thunderbird 1.0.5, the old extensions may cause errors at runtime of the newer version. To alleviate this, exclude (uncheck) "Extensions" on the "Select the details you want to restore:" page. You will have to reinstall new versions of the extensions from the Mozilla Update Site.
Mozbackup supports command line arguments to specify what it should back up. This means you can schedule backups using the Windows task scheduler. See this web page for more information.
Problems restoring with MozBackup?
If you get a "Zip file could not be opened" error message use 1.5 alpha1 of Mozbackup to restore it. This is a known problem that should be fixed in version 1.5 of Mozbackup.
If you are having problems restoring a ".pcv" backup file that you created with MozBackup and nothing seems to work, keep in mind that the ".pcv" file is actually a normal ".zip" file.
Your unzip utility will do a CRC check of the files within the .zip file. If they don't match it will report the .zip file is corrupt, and won't let you extract them. If this happens try using a program such as DiskInternals ZIP Repair.
How to set the default folder for backup files
If you want to set the default folder for your backup files, go to the MozBackup program folder and find the file named "backup.ini". In this file you can set the default backup folder, as a general setting and/or for specific Mozilla applications.