Thunderbird 6.0, etc.

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In a process driven by the Firefox developers, Mozilla has substantially redesigned their release process [1]. Thus, there will no longer be parallel branches after Firefox 3.6 and Thunderbird 3.1 have reached their end of support. Instead, each release will have a full version bump even if there are no or marginal feature changes (i.e., Firefox 5.0 will be the stability update for 4.0.1, then 6.0 will be the update for 5.0, etc.) [2]. Only in quick "firedrill" follow-up releases which become necessary shortly after a release to fix a missed issue, a minor "dot" release will be issued.

Thunderbird decided to follow that pattern [3], and in the process to re-align its numbers with Firefox again [4]. Consequently, the "Miramar" branch has been bumped from 3.3 to 5.0, and the next release after 5.0 will be Thunderbird 6.0 (formerly 3.4) around the same time when Firefox 6.0 is released. It yet has to be seen how this process turns out in practical terms, especially with respect to add-on compatibility as a stable API is no longer given as it was previously assured during the lifetime of a branch.

The user-facing changes between Thunderbird 5.0 and Thunderbird 6.0 should be close to none, given that there were only two weeks (May 10 vs. May 24, 2011) between the string and feature freezes of these two versions, even if the time between those two releases is longer.

In the following sections, updates to the previous articles should be added along with a reference to the respective section in that article which they obsolete. This is intended to keep track of any incremental changes as development of new features and bug fixes proceed. If a change checked into multiple branches at the same time, it is listed for the first release version where it becomes active.

This page is not intended to track all changes from version to version, this would be way to much work. It provides updates to previous issues and highlights new features or problems which may have a high visibility, along with workarounds if available. Note that there are also detailed tracking lists now on the Mozilla Wiki, to which links are provided in the individual update sections.

Updates for Thunderbird 6.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 6

New appearance on Windows 7 and Vista

relates to section: Thunderbird 5.0 - New Features and Changes#New appearance on Windows 7 and Vista

A regression has been fixed where with the Windows 7 Default and Basic themes (and possibly other desktop themes on windows) drag-and-drop of a message into a folder would not highlight the selected folder as drop target [5].

A mitigating fix for the poor visibility of menus and toolbar buttons on dark desktop themes, caused by the use of aero glass in that UI elements, has been checked in to decrease the transparency for those items [6]. An alternative is the NoGlass ass-on [7], which removes the glass effect entirely. An extensive discussion on the use of aero glass and various other tips and workarounds can be found in a GetSatisfaction topic [8].

The IgnoreAero theme provides 3.1-style appearance for 5.0 and should equally work for the later versions [9].

Folder and message list spacing

If your Start → Control Panel → Display settings are set to Medium (125%) or Larger (150%) text size, folder labels and message-list entries may have been cut off at the bottom in 5.0 [10]. The spacing was changed in 6.0 to be based on that size rather than fixed for all font sizes, now in turn leaving a larger spacing between list entries [11], [12]. You can revert that change using the following userChrome.css code:

listitem, treechildren::-moz-tree-row {
  min-height: 20px !important;

Font rendering and performance issues

relates to section: Thunderbird 5.0 - New Features and Changes#Font rendering and performance issues

The options to influence ClearType/Direct2D have been extended with the following preferences, thus allowing a better fine-tuning of font display [13], [14], [15]:

  • gfx.font_rendering.cleartype_params.gamma - between 1000 and 2200 and describes a luminance curve, the value depends on the physical screen characteristics
  • gfx.font_rendering.cleartype_params.enhanced_contrast - 0 to 1000, the default 50 should work for black on white
  • gfx.font_rendering.cleartype_params.cleartype_level - 0 to 100 (percent?), defaults to 100, where 50 is recommended for a compromise in fringe effects
  • gfx.font_rendering.cleartype_params.pixel_structure - 0 to 2, defaults to 0 = "flat" but may be set to 2 for BGR monitors (this seems to influence the shift between red and blue colors)
  • gfx.font_rendering.cleartype_params.rendering_mode - the value 0 means default handling depending on font and size, other values:
    1. aliased
    2. GDI Classic
    3. GDI Natural Widths
    4. Natural
    5. Natural Symmetric

The defined defaults for all preferences is "-1" and implies the stated default behavior.

Another preference gfx.font_rendering.cleartype_params.force_gdi_classic_for_families contains a comma-separated list of fonts for which GDI classic mode will be used, up to a size specified in the .force_gdi_classic_max_size preference and only if .cleartype_params.rendering_mode doesn't specify a non-default behavior.

Adding links to HTML messages

relates to section: Thunderbird 5.0 - New Features and Changes#Images and links in HTML messages

When composing a new message and using the Insert → Link function, pasting a web address into the Link Location field using the right-click menu was broken. This function has been restored in TB 6.0 [16], [17].

Printing headers

Due to a regression from localizing the "Date:" headers for printing in 5.0, dates were missing by default when printing e-mails on the date they were sent [18], [19]. This is fixed in 6.0 beta 3.

Updates for Thunderbird 7.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 7

Attachment pane redesign: Menu issues

relates to section: Thunderbird 5.0 - New Features and Changes#Attachment pane redesign

There have been some inconsistencies in disabled/enabled status for the menu items in File → Attachment, the attachment-bar menu, and the attachments' right-click context menus. That part has been rewritten to show the expected menu items being available [20].

Phoning home: Telemetry

relates to section: Thunderbird 5.0 - New Features and Changes#Phoning home

While technically already implemented in TB 6.0, the official server to collect telemetry data on performance of Mozilla applications went in effect with Gecko 7.0 [21], [22]. By default, telemetry/performance is switched off and has to be enabled by the user (who gets prompted in TB 9.0 and after to opt in).

Related preferences:

  • toolkit.telemetry.enabled - activate performance reporting to Mozilla, set "false" to disable
  • toolkit.telemetry.server - server to report to, defaults to

Updates for Thunderbird 8.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 8

Folder Pane / Smart Folders

relates to section: Thunderbird 3.0 - New Features and Changes#Smart Folders

The header over the folder pane allowing to cycle between Smart/Unified Folders, All Folders, and other views is no longer available by default, thus they have to be selected from the View → Folders menu [23]. That header bar is just hidden though and can be reactivated by the userChrome.css code below, or by using the Folder Pane View Switcher add-on which also provides additional folder-view options [24].

#folderPaneHeader, #abDirTreeHeader {
  display: -moz-box !important;

Quick-Filter Bar: New keyboard shortcuts

relates to section: Thunderbird 3.1 - New Features and Changes#Quick-Filter Bar

The keyboard shortcut Ctrl+F, previously used for both the Quick-Filter Bar and Find in This Message has been changed to Ctrl+Shift+K for the Quick-Filter Bar (in analogy to Ctrl+K for the Gloda search) [25]. Ctrl+F now performs exclusively Find in This Message, whereas the ESC key closes one or the other depending on the mouse focus.

Here a summary of search-related keyboard shortcuts:

  • Find in This Message – Ctrl+F (back to previous function)
  • Search Messages window – Ctrl+Shift+F
  • Find Again, Next – Ctrl+G
  • Find Again, Previous – Ctrl+Shift+G
  • Global-Search Bar – Ctrl+K
  • Quick-Filter Bar – Ctrl+Shift+K (new)

Images and related content in HTML messages

relates to section: Thunderbird 5.0 - New Features and Changes#Images and links in HTML messages

Attachments in a "multipart/related" context (such as images inserted into the message body itself, but also items like PDF files which Thunderbird cannot display inline) are no longer provided in the attachment pane even if View → Message Body As → Plain Text is chosen [26].

A hidden preference mailnews.display.show_all_body_parts_menu has been introduced, which – if set to "true" – provides a new menu item View → Message Body As → All Body Parts. Select this to present all MIME parts of the message as attachments, which will be displayed if they can be shown inline unless View → Display Attachments Inline in unchecked. This allows to (a) save again embedded content from the attachment pane, and (b) access attachments in a malformed message which otherwise would stay invisible.

There is also an add-on [27] which can be installed to enable the additional menu point. It was mostly created for easier identification and documentation of that feature [28]. Note that the add-on won't work in versions prior to 8.0.

Message header pane: Gaining vertical space

relates to section: Thunderbird 3.1 - New Features and Changes#Gaining Vertical Space

If you are hiding the header-pane toolbar buttons using the suggested userChrome.css code, you will notice an additional 10px space over the "from:" heading now with 8.0 caused by a new expandedBoxSpacer box [29]. Since this box isn't needed when you hide the toolbar, extend the code by an additional entry to regain that space:

#header-view-toolbox, #otherActionsButton {
  display: none !important;

#expandedHeaderRows {
  padding-top: 0px !important;

#expandedBoxSpacer {
  height: 0px !important;

Of course, you can pick values other than 0px to have some space between the message/thread list and the headers.

Attachment pane redesign: Open expanded

relates to section: Thunderbird 5.0 - New Features and Changes#Attachment pane redesign

The attachment pane in the message viewer has been redesigned substantially [30]. If you are using the suggested userChrome.css code to open the attachment pane fully expanded by default (2nd block in that section), it does no longer work but will just open one line of attachments. You'll need to compensate for the new scrollbox that has been introduced in the binding and keep it from scrolling. Thus, the full CSS code to open the box in full and to hide the toggle is:

#attachmentList > scrollbox {
  overflow: visible !important;

#attachmentView > [collapsed="true"] {
  visibility: visible !important;

#attachmentToggle {
  display: none !important;

Attachment pane redesign: Large icons

relates to section: Thunderbird 5.0 - New Features and Changes#Attachment pane redesign

The boolean mailnews.attachments.display.largeView preference has been deprecated and replaced by an integer preference mailnews.attachments.display.view [31]. There doesn't appear to be any migration code initializing it to reflect your previous choice [32], defaulting to "small" again. The following values are available:

  • 0 — small icons left to the attachment name, size to the right of the name
  • 1 — large icons left to the attachment name, size underneath the name
  • 2 — large icons on top of the attachment name with size underneath

Updates for Thunderbird 9.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 9

Hide the menu bar on Windows

relates to section: Thunderbird 5.0 - New Features and Changes#New appearance on Windows 7 and Vista

As already possible in Firefox, the menu bar can be hidden with View → Toolbars → Menu Bar [33]. Once unchecked, the menu toolbar can be temporarily shown by hitting the "Alt" key. Note that this feature is not available on Mac OSX or Linux platforms.

Hardware acceleration disabled

relates to section: Thunderbird 5.0 - New Features and Changes#Font rendering and performance issues

By default, layers.acceleration.disabled and gfx.direct2d.disabled are now set to "true", thus avoiding many performance and rendering issues seen on certain platforms [34].

Opt-in UI for Telemetry

relates to section: Thunderbird 5.0 - New Features and Changes#Phoning home

Users are now prompted to opt into telemetry/performance reporting to Mozilla [35]. A new preference setting toolkit.telemetry.prompted keeps track of that and switches to "true" once the user has made a choice.

Updates for Thunderbird 10.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 10

Attachment display and handling

relates to section: Thunderbird 5.0 - New Features and Changes#Attachment pane redesign

In the composition window, a new keyboard shortcut Ctrl+Shift+A can be used to add an attachment to outgoing messages [36]. As a result, the prior "Remove named anchors" keyboard shortcut changed to Ctrl+Shift+R.

When displaying a message, attachments are no longer forced into a fixed-size grid in the attachment pane at the bottom of a message, thus no longer truncating long file names as long as they fit into the window width [37]. However, the grid is still present, it's adjusting to fit the longest file name. This may lead to one attachment being listed per row in the extreme case, without being able to restrict the overall size of an attachment entry [38].

Note that if you use the userChrome.css code to keep the attachment pane open at all times as updated above, the grid is initially not enforced and all attachment are using the horizontal space they need until a row is filled (corresponding to an "auto" size). Only when you click on the attachment button they will be aligned to the grid.

If you prefer the old fixed-size grid, you can revert to the previous spacing with the following userChrome.css code:

attachmentlist[orient="horizontal"] attachmentitem {
   width: 15em !important;

Performance: Schema change in Gloda

relates to section: Thunderbird 3.0 - New Features and Changes#Searching

There has been a change in the Gloda database schema with this update, requiring the Gloda database to be purged and all messages reindexed [39]. Depending on the number of accounts, folders, and messages, as well as the performance of your hardware, this may take a while and consume considerable resources in CPU and disk usage.

Fortunately, this is a one-time event, but may happen again if a later version changes the database schema again.

New feature: Search the web

When highlighting a word or phrase, the right-click context menu will offer now a "Search the web for ..." option [40]. This is functionality originally provided by the OpenSearch add-on [41]. In Thunderbird 10.0, the search engine defaults to Google.

If you prefer the search to be performed externally in your default browser, set the mail.websearch.open_externally preference to "true".

Updates for Thunderbird 11.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 11

Tabs on top

relates to section: Thunderbird 3.0 - New Features and Changes#Message and Folder Tabs

The most noticeable change in this update is that the main toolbar has been moved into the tab box, thus the tabs are now on top of the toolbar similar to respective changes made for Firefox [42]. This is a mandatory change though, thus there is no option provided to move the toolbar above the tabs again as in Firefox [43]. While the developers argue in that bug against such a configuration option, an add-on has been developed which moves the toolbar outside the tab box again as an interim fix [44].

It is unclear at the time of writing how exactly the toolbar will be made sensitive to the content of a specific tab, given that thus far only the 3-pane window, a message tab, and the Gloda-search tab have toolbars, and those are currently shared [45], [46]. This should become more concrete when compose in a tab [47] and address book in a tab [48] are approached which will require such context-specific changes in the toolbar.

Menus below tabs on Windows 7 and Vista

relates to section: Thunderbird 5.0 - New Features and Changes#New appearance on Windows 7 and Vista

When using "aero" themes, the menu bar now moves into the tab box, thus the menus are located between the tabs and the main toolbar [49]. While this resolves long-standing issues with the readability of the menus on the transparent ("glass") background [50], users may find it irritating and want to switch the menu bar back above the tabs (especially when not using an aero-glass theme).

In general, this is just a matter of the ordinal grouping and can be changed one way or the other using userChrome.css overrides:

To force the menu bar to be located within the tab box:

#tabs-toolbar {
  -moz-box-ordinal-group: 10 !important;

#mail-toolbar-menubar2 {
  -moz-box-ordinal-group: 20 !important;

To force the menu bar to be located above the tab box:

#tabs-toolbar {
  -moz-box-ordinal-group: 20 !important;

#mail-toolbar-menubar2 {
  -moz-box-ordinal-group: 10 !important;

Show attachments even in wrong context

relates to section: Thunderbird 5.0 - New Features and Changes#Attachment pane redesign

With Thunderbird 5.0, the criteria for whether or not to offer a message part in the attachment pane for the user to access were made more restrictive, resulting in some messages putting attachments wrongfully into a multipart/related context no longer shown [51], [52].

More of such attachments should now be accessible directly without the need to use the View → Message Body As → All Body Parts workaround being necessary. Specifically, attachments in such a context which have a file name or those with an explicit disposition as attachment should be shown now.

Search the web: Google removed

In Thunderbird 11.0, Google has been removed from the list of available search engines for the new "Search the web for ..." feature and replaced by Bing [53]. The short reason given by Thunderbird marketing is that "The Thunderbird default list of search engines reflects the agreements and authorizations we have with their respective owners. We do not have such agreement or authorization from Google" [54].

A "Google Search for Thunderbird" extension is provided to make Google available as search engine again and also sets it as the default [55].

Alternatively, there is also a manual workaround available though to add back Google as a search engine: [56]

  1. Go into your profile folder
  2. create a directory named "searchplugins" if it does not already exist
  3. add the following code to a new text file google.xml in that folder with the following content [57]:*
<SearchPlugin xmlns="">
<Description>Google Search</Description>
<Image width="16" height="16"></Image>
<Url type="application/x-suggestions+json" method="GET"
<Url type="text/html" method="GET" template="">
  <Param name="q" value="{searchTerms}"/>
  <Param name="ie" value="utf-8"/>
  <Param name="oe" value="utf-8"/>
  <Param name="aq" value="t"/>

Restart Thunderbird and search for something, then click the Google icon on the side. Click the little heart at the bottom to make it your default search engine.

  • Note: Windows users may find that the line endings don't work when using an editor like Notepad [58]. Also make sure that the last line has a proper ending. If you don't have an editor that allows you to use LF rather than CRLF line endings, just download the XML file from the given link directly.

Migrating old profiles

Migration/importing of old profiles from Netscape 6.x/7.x, Mozilla Suite 1.x, or SeaMonkey 1.x has been removed with Thunderbird 11.0 (this also applies to SeaMonkey 2.8 and later) [59]. To migrate such profiles, use either Thunderbird 3.x or SeaMonkey 2.0 to import the old profile, then update to the most recent Thunderbird version from there. As always, make sure to have a profile backup before getting started so that you can roll back to the original state.

Updates for Thunderbird 12.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 12

Gloda search / Performance issues

  • Gloda search now shows the part of the message that matches the search term [60].
  • If you notice a substantial lack of performance after updating to 12.0/12.0.1 (especially from a version prior to 10.0), check your profile folder for the existence of ".sqlite-shm" and/or ".sqlite-wal" folders (not regular files) and remove them [61]. This may affect sqlite files other than global-messages-db.sqlite, primarily places.sqlite or cookies.sqlite have been reported.

Backend: Pluggable mailstores

  • A new major feature are "pluggable mailstores" [62], which however caused a regression with persistent/repeated new-mail notifications for POP accounts which are set to leave the messages on the server [63]. This and other issues are fixed in TB 12.0.1.
  • The mail backend has been extended by the "maildir" format in addition to the traditional "mbox" format [64], [65], [66]. A new preference mail.serverDefaultStoreContractID determines the format to be used. This defaults to "berkeleystore" which is the previously exclusively used "mbox" format, thus there shouldn't be any impact from the user's perspective at this time.
  • To enable the maildir format for new accounts, set mail.serverDefaultStoreContractID to;1 (there is no UI for any of this yet).
  • Note: Running TB 12 with local mail folders and pop3 mail filters may produce summary files that aren't correctly read by previous versions of Thunderbird. If you decide to go back to a previous version of Thunderbird after running TB 12, you should delete the .msf files for your local folders and pop3 accounts, or repair the folders using the folder properties dialog, to avoid potential data loss.

Persistent pop-ups to compact folders

  • There have been various reports about the dialog suggesting to compact folders after deleting messages, on an approximate hourly interval despite the threshold set in the Advanced → Network & Disk Space options not yet reached [67].
  • The reason is yet unknown, in some instances using the "Repair Folder" function in the right-click menu "Properties" worked after applying it to all folders. If not, switching off the "Compact folders when it will save over..." function may be the only way to get rid of that dialog for now.

Updates for Thunderbird 13.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 13
  • Support for Windows 2000 has been dropped in Gecko 13.0, and at least SP2 is needed for Windows XP [68], [69].
  • A major new feature is "Attachment in the cloud" allowing large attachments to reside with file services rather than being physically attached to the message [70]. Currently, Dropbox [71] and YouSendIt [72] are supported.
  • Instant Messaging is another major feature addition [73] which essentially integrates the Instantbird [74] code, a Gecko-based stand-alone IM application.
  • Both features are currently in the Beta builds, but may still be buggy and caused a couple of regressions which are hopefully cleaned up until they hit the release channel. They can be enabled or disabled with the mail.cloud_files.enabled and preferences.
  • Instant messaging is preffed off by default in 13.0 [75] to finalize some features, thus needs to be activated first. Its conversations are logged unless purple.logging.log_ims (private conversations) and/or purple.logging.log_chats (multi-user chats) are toggled [76].

Updates for Thunderbird 14.0

related Mozilla Wiki page: User Visible Changes to Thunderbird 14
  • Currently in the Earlybird nightly builds, Instant Messaging remains enabled by default for feedback [77].

See also