Files and folders in the profile - Thunderbird

This article is a supplement to Profile_folder_-_Thunderbird that provides more details about the files and/or folders used by Thunderbird's profile.

Files

None of these files should be read-only. If they are that might be a side effect of dragging and dropping or backing up files to removable media, and then using them to restore your profile.

Name	Description
.autoreg	Temporary empty file that signals a change in the installed extensions.
.parentlock	See parent.lock
abook.mab	Personal Address Book
blocklist.xml	Added list of dangerous extensions.
cert8.db	Security certificates
compatibility.ini	Stores version and path of the application this profile was last used with. When the profile is loaded with an application of a different version/path, the XPCOM components registration process is triggered. This file is automatically generated and can safely be deleted.
components.ini	Lists extension folders with XPCOM components. Replaced with extensions.ini in 1.5.
compreg.dat	Lists registered XPCOM components. Automatically regenerated whenever XPCOM registration process is triggered.
cookies.txt	Cookies RSS_cookies_(Thunderbird)
cookies.sqlite	Cookies used by Lightning extension
downloads.rdf	Download history. Can be deleted to resolve slow downloads or program hangs (Bug 159107)
extensions.cache	Lists installed extensions, their IDs, and the folders they are installed to, along with their last-modify time. It is used, for example, to register extensions installed by dropping a folder into one of known install locations. This file is automatically regenerated and can be deleted to resolve various issues.
extensions.ini	Lists folders of installed extensions and themes. The file is automatically generated by nsExtensionManager and is used by low-level code to detect chrome packages and XPCOM components provided by installed addons. It can be deleted to resolve various issues.
extensions.rdf	Installed extension information. It can be deleted to remove "ghost" entries from the extension list [1] and to resolve various other issues.
filterlog.html	Message filter log. If filter logging is enabled its stored in the accounts directory.
history.mab	Collected addresses
hostinfo.dat in News	Contains all the newsgroups available for the current server
junklog.html	Junk mail log for that account
key3.db	Key database
localstore.rdf	Toolbar and Window_layout_-_Thunderbird window size/position settings. It can be deleted to resolve various issues.
localstore-safe.rdf	Special version of localstore.rdf used in Safe Mode to set toolbars and window customizations to defaults. [2]
lock (Linux)	See parent.lock
mailviews.dat	Defines your current message view (you can customize it)
menuedit.rdf	Used by MenuEdit extension
mimeTypes.rdf	Action to perform when downloading certain types of files. Can be deleted to reset download actions.
msgFilterRules.dat in ImapMail, Mail, News	Message filters
nsmail.eml, nsmail.tmp, nsmail.html	Temporary files created when sending a message.
nstmp	Thunderbird creates a nstmp temporary file when compacting a folder. You should not see it (or nstmp-1, nstmp-2 etc.) unless Thunderbird was interrupted while compacting.
panacea.dat	Mail folder cache
parent.lock	Marker showing that the current profile is in use. Can be deleted to unlock the profile.
persdict.dat	Personal spelling dictionary
permissions.sqlite	Used by Lightning extension
popstate.dat in Mail	Keeps track of which messages have been left on the POP3 server
prefs.js	All preferences. See: Modify Thunderbird settings
secmod.db	Security module database
signons.txt	Encrypted saved passwords, requires key3.db to work
storage.sdb	Internal calendar data (in SQLite format) if you use the Lightning extension
training.dat	Custom training for Junk Mail Controls
tmprules.dat	Temporary file used when modifying message filters.
user.js (does not exist by default)	User-set overriding preferences
userChrome.css in chrome (does not exist by default)	User-set CSS to change the way the application looks
userContent.css in chrome (does not exist by default)	User-set CSS to change the way webpages look
userChrome.js in chrome (does not exist by default)	User-set JavaScript to change the way the application works
virtualfolders.dat	Saved Search folder settings
xpti.dat	Lists registered XPCOM interfaces. Automatically regenerated whenever XPCOM registration process is triggered.
XPC.mfl	A cache file for components (XPC)
xul.mfasl	The Linux version of the XUL.mfl file
XUL.mfl	Cached user interface data. Can be deleted to resolve various issues (file location changed in Thunderbird 1.5 [3])
XUL FastLoad File	See XUL.mfl

Files without specific names

Name	Description
(number).s	Obsolete. It used to be used for saving passwords. The "(number).s" value was specified by the signon.SignonFileName preference.
*. in ImapMail, Mail, and News	Mbox files. They are text files that contain all of the messages for that folder.
*.mab other than abook.mab and history.mab	User-created or imported address books.
*.msf in ImapMail, Mail, and News	Index files for mail messages.
*.rc in News	Subscribed groups.

Files outside the profiles folder

Name	Description
pluginreg.dat	Registration of plugin mimetypes. Its located in the "Thunderbird" folder containing the profiles. Its very unusual to have any plugins.
profiles.ini	Keeps track of the profiles location. Its located in the <parent> folder containing the "Profiles" folder, and can be edited to point to a moved profile folder. If deleted, profiles.ini will be regenerated along with a new default profile folder upon program restart.
registry.dat	Obsolete. Keeps track of where your profiles are located. It's located in the "Thunderbird" folder containing the profiles.

You can store messages outside of the profile by configuring Thunderbird to store an accounts directory outside of the profile. If you do that you need to move the directories yourself, modifying the preferences in prefs.js just tells Thunderbird where to look for the files.