How do I recover saved passwords from Thunderbird?
Tools -> Options (Windows) | Edit -> Preferences (Linux) | Thunderbird -> Preferences (OS X) ->
Security > Passwords > Saved Passwords
There you are given an option to reveal email passwords. Eek!
Thunderbird stores account passwords in a database table with the text encrypted all inside your Thunderbird profile directory.
If you are curious, you can use SQLite Database Browser (Mac / Win / Linux) to open the database file which contains the login text.
Navigate to and open the signons.sqlite file located in your Thunderbird profile directory and it will contain a table moz_logins. Your base64 encrypted username and passwords are there.
Note: You can set a Master Password for Thunderbird for added security. I highly suggest this!
PS: There is an excellent Windows freeware tool here as well for recovering Thunderbird passwords which can read any profile directory (Mac, Windows, Linux).