Files and folders in the profile - Thunderbird

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This article is a supplement to Profile folder - Thunderbird and provides more detail about files in the Thunderbird profile folder.

A good rule of thumb is that it is okay if you have a few strange files in your profile since they are probably either due to an add-on or this article not being updated yet, but any time you find a SQLite file replaced by a directory with the same name its probably due to a bug.


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 (Mac OS X) See parent.lock
abook.mab Personal Address Book
addons.sqlite Used by add-ons manager.
blocklist.xml Added list of dangerous extensions.
cert8.db Security certificates
cert_override.txt This is an optional file used to store a security exception. It appears to store the host name , thus preventing you from creating a security exception for a rotating SMTP server.
chromeappsstore.sqlite Unknown. There is a similar file in Firefox profiles used by localstorage/DOMStorage to store about: pages. [1]
compatibility.ini Stores the version and path of the application this profile was last used with. When the profile is loaded with an application with a different version/path, the XPCOM components registration process is triggered. Thunderbird 3.x appears to use the version information to decide whether to display additional tabs such as the migration assistant and whats new. This file is automatically generated and can safely be deleted.
components.ini Lists extension folders with XPCOM components. Replaced with extensions.ini in Thunderbird 1.5 and above.
compreg.dat Lists registered XPCOM components. Automatically regenerated whenever XPCOM registration process is triggered.
custom-strings.txt in chrome
(does not exist by default)
It can be used to replace text in the user interface. [2]
cookies.txt Cookies RSS cookies - Thunderbird
cookies.sqlite Cookies used by Lightning extension
cookies.sqlite-journal Journal file for cookies.sqlite
cookies.sqlite-shm , cookies.sqlite-wal write-ahead log files for cookies.sqlite
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 safely deleted to resolve various issues.
extensions.log Records some errors reported by the Extension Manager.
extensions.rdf Installed extension information. It can be deleted to remove "ghost" entries from the extension list [3] and to resolve various other issues.
extensions.sqlite Stores data about installed extensions, not clear yet if it replaces or supplements the extensions.rdf file.
feeds.rdf Stores your RSS subscriptions. Its in in the Mail\feeds directory
feeditems.rdf Records RSS feeds. Its in in the Mail\feeds directory
filterlog.html Message filter log. If filter logging is enabled its stored in the accounts directory.
foldertree.json Used by the folder pane.
global-messages-db.journal rollback transaction journal for global-messages-db.sqlite (temporary file)
global-messages-db.sqlite An index of all of your messages created by the global search engine (gloda). Can be deleted if db is corrupt or search isn't working correctly - it will be rebuilt.
history.mab Collected addresses address book
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 and size/position settings. It can be safely 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. [4]
lock (Linux) See parent.lock
mailviews.dat Defines your current message view (you can customize it)
menuedit.rdf Used by Menu Editor 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. It can be safely deleted to resolve various issues.
parent.lock (Windows) 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
places.sqlite-shm, places.sqlite.wal Write-ahead log files for places.sqlite. You should not have a places.sqlite-shm and a places.sqlite.wal directory (instead of files with that name). If you do that causes Thunderbird to be extremely slow. Its not clear what creates them, but the workaround is to delete those two directories. [5]
popstate.dat in Mail Keeps track of which messages have been left on the POP3 server
prefs.js All preferences, including account settings and mail folder locations. See: Modify Thunderbird settings
pubring.gpg Public keys (yours and any you collected) for the Enigmail (OpenPGP) extension.
rulesbackup.dat If msgFilterRules.dat can't be read it backs it up in that file and creates a new msgFilterRules.dat.
search.json Not clear what it is since there is no search.sqlite to cache. [6]
secmod.db Security module database
secring.gpg Private keys for the Enigmail (OpenPGP) extension.
session.json Default windows layout. Thunderbird 3.x deletes this file after reading the settings. Its re-created and the layout saved when Thunderbird 3.x terminates normally.
Signons.sqlite Encrypted saved passwords, requires key3.db to work. It used to use signons.txt or signons3.txt.
storage.sdb Internal calendar data (in SQLite format) if you use the Lightning extension
training.dat Custom training for Junk Mail Controls
traits.dat Bayes traits training data used by the TaQuilla add-on
tmprules.dat Temporary file used when modifying message filters.
Unsent Messages. The "Unsent Messages." mbox file in ..\Mail\Local Folders is displayed as the Outbox folder by recent versions of Thunderbird. That folder is used to queue unsent messages if you use "Send Later".
urlclassifier2.sqlite Contains information on known phishing sites. Obsolete.
urlclassifier3.sqlite Contains information on known phishing sites. Seems to be a replacement for urlclassifier2.sqlite, which replaced urlclassifier.sqlite.
(does not exist by default)
User-set, overrides the preferences in prefs.js
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 (Linux) See XUL.mfl file
XUL.mfl (Windows) Cached user interface data. Can be deleted to resolve various issues.
File location changed in Thunderbird 1.5. [7]
XUL FastLoad File (Mac OS X) 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 (no file extension) 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.
*.mozeml Each file is a partial copy (up to 20kb) of a message in the mail folder, stored in a .mozmsgs subdirectory. Used by the optional Spotlight Integration component under OSX. It's deleted when the message in the mbox is deleted. [8]
*.rc in News Subscribed groups.
*.tha The MoreFunctionsForAddressBook add-on uses this file extension for contacts.
*.thm The MoreFunctionsForAddressBook add-on uses this file extension for mailing lists.
*.wdseml Copies of messages (its actually a .eml file) created by Windows Search Integration (requires Vista or Windows 7). They're stored in .mozmsg directories.
*.xpi in Extensions .xpi files are renamed .zip files used by add-ons. Usually they're unzipped and the files stored in a child directory (its name is the GUID that uniquely identifies that add-on) when the add-on is installed but some (such as IgnoreAero and Add-on Compatibility Reporter) aren't.

Files outside the profile folder

Name Description
application.ini The installation directory has an application.ini file with general information about what build you are using and additional entries that control whether the profile manager and extension manager are enabled.
custom-strings.txt File in the chrome subdirectory in the programs installations directory used to replace strings. [9] [10]
MozillaMailnews Directory in temporary files directory.
Updates ..\Local Settings\Application Data\Thunderbird\Mozilla Thunderbird is the directory used to store updates when upgrading, under Windows. This is not the same directory tree as %APPDATA%. Its underneath C:\Documents and Settings\user_name on XP, and user_name\Appdata on Vista. Similar directories are created for other operating systems.

It has a "active-update.xml" file plus a updates subdirectory with numbered sub-directories (usually "0"). If an update gets caught in a loop you can break the cycle by deleting "active-update.xml" plus the numbered subdirectory with the updates. Thunderbird (so far) re-creates that Mozilla Thunderbird directory tree as needed if it doesn't exist.

omni.ja It contains most of the default preference files that used to be stored in in the defaults\pref subdirectory in the Thunderbird program directory such as mailnews.js all-thunderbird.js. Its in the root of the program directory. Its contents can be viewed using any program that knows how to open a .zip archive file. It used to be called omni.jar but was renamed because Window’s System Restore does not backup .jar files. [11]
pluginreg.dat Registration of plugin MIME types. It's located in the "Thunderbird" directory containing the profiles.
profiles.ini Keeps track of the profile folder location. It's located in the "Thunderbird" directory containing the profiles. It 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 profile folder location in previous Thunderbird versions. It's located in the "Thunderbird" directory 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.