Thunderbird makes it very easy for you to backup all your current emails, email account settings and rules filters all in one go, unlike Outlook and Live mail, to name but a couple.
There are no settings stored in the Registry File or in a database on your system, everything is stored in 1 folder on your pc which you can copy to an external drive or even burn it a cdr/dvdr. If you have created extra Profiles after installing Thunderbird, then you will just need to copy each Profile separately.
The Profile is stored in different places depending on your Operating Sytstem, below will give you a rough guide:-
If you cannot find your Thunderbird Folders it may be a good idea to read this article for further help:-
The first thing you have to make sure of is that you have Windows Explorer set to view Hidden Files, you can do this by running Explorer and from the Tool Bar select View / Folder Options --> Show hidden files and folders. Once you have done this you should be able to see something similar to the image below, this one is for Windows 8, but Vista and 7 will be almost the same.
All you need to do now is select the folder, or folders if you have created any extra Profiles, then copy and paste to any external drive or USB stick it is that easy.
If you have had a problem with Thunderbird, or wish to transfer them to another pc, all you have to do is copy the backed up Profile and copy it back to it's original location.
Another way is to use MozBackup - this is a Freeware programme and can be used to backup and restore bookmarks, mail, contacts, history, extensions, passwords, cache etc. easily.