Thunderbird 5.0 - New Features and Changes

From MozillaZine Knowledge Base

Thunderbird 5.0 has been released on June 28, 2011.


What happened to Thunderbird 4.0?

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 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.

Changes in supported platforms

There are no changes in support on Windows, the minimum platform remains Windows 2000 and only 32-bit builds are available [5].

On Mac OSX, support for 10.4 is discontinued, and the PPC platform (G3, G4, G5) is no longer supported. Instead, the universal downloads contain both 32-bit and (new) 64-bit versions for Intel Macs.

Linux requirements are the same as for 3.1; by default you will get the 32-bit version from the download page, official 64-bit builds are available from the release server for manual download [6].

New appearance on Windows 7 and Vista

TB 5.0 aero theme over Windows 7 Default desktop theme

New default theme

While the "aero" theme has received a major overhaul [7], only moderate updates have been made to the themes on the other platforms, including the Windows XP/2000 theme. See Thunderbird 5.0 - New Features and Changes/Themes for a detailed discussion on the changes on Windows 7 and Vista. Most notably, the new default theme doesn't work well for aero themes with a dark background [8], [9]. Note: Mitigating changes were made for Thunderbird 6.0.

There has been a redesign of the addressing area in the composition window on all platforms [10]. As the most visible change, the "To", "Cc", ... selector buttons are no longer part of the address block but appear as "real" menu buttons to the left of it.

On Linux, the default theme uses several GTK stock icons, i.e., they aren't included with the Thunderbird default theme. You may see error messages in your console window that icons are missing, and those may not display properly when Thunderbird is running. Thus, make sure that the relevant GTK libraries are installed. Using a re-packaged Thunderbird version from your distribution's repository may avoid any such conflicts.

Font rendering and performance issues

Like Firefox 4.0 and later, Thunderbird 5.0 supports hardware acceleration and (on Windows) Direct2D font rendering [11], which are switched on by default [12]. These are supposed to increase graphics performance and text quality, but depending on your specific hardware and driver configuration, may actually cause slowing of the overall system and fuzzy-font problems as various reports indicate [13], [14]. You can check in Help → Troubleshooting Information, Graphics section at the very bottom, if either is active on your system (look for "Direct2D Enabled" and "GPU Accelerated Windows" where the first number is greater than zero if any window uses hardware acceleration). This section may also provide possible hints, e.g., on an outdated driver.

If the fonts look blurred to you (and won't improve with tweaking the ClearType settings on Windows as explained below either) and/or you see substantial decrease in overall performance, change gfx.direct2d.disabled to "true" and then restart to see if it makes any difference. If this doesn't solve the issue, switch off hardware acceleration by setting the layers.acceleration.disabled preference to "true" and then again restart Thunderbird. Toggling other layers.prefer-* preferences may mitigate rendering issues as well. More preferences are expected with Thunderbird 6.0.

Most platforms in general perform font smoothing by default to achieve a better rendering on LCD screens, this applies equally to all applications and isn't unique to Thunderbird. On Windows 7, this is ClearType [15] and can be modified in the Display section of the Control Panel ("Adjust ClearType text"). Depending on your personal preferences or needs, different settings may work better for different users, thus it's a bit of try and error to find the optimum settings.

Account setup

New account wizard

After substantial criticism on the original implementation of the account wizard, it has been reimplemented to a large extent in Thunderbird 5.0 and resolves a couple of issues seen with the 3.0/3.1 wizard [16]. Performance has been improved in the "guessing" algorithm to try the various options in parallel rather than one by one [17]. Also, if both IMAP and POP configurations are available, it is now easily possible to pick one or the other [18], [19]:

TB 5.0 result of Account Wizard for Gmail account

Note that once an account has been established as either IMAP or POP type, it can't be switched to the respective other type without recreating the account, this hasn't changed.

While it is still not possible to start a completely manual setup from scratch (the argumentation being that a configuration known in Mozilla's ISP database should be more accurate than frequently wrong information given by the providers themselves), the "Manual Config" button can now be pressed at any time to abort the auto-configuration process and to enter the manual setup. The account wizard requires that the servers are responsive in either case, thus it's still not possible to set up an account manually while off-line or if the server isn't available for any other reason [20].

Archiving can be disabled

Thunderbird 5.0 now allows disabling the "archive" function if not desired, along with the "A" keyboard shortcut, message-header button, and menu item [21]. This option is available on a per-account basis by unchecking a new box in the Copies & Folders Account Settings [22]:

TB 5.0 new Archive settings with enable box and options button

When pressing the "Archive Options" button (not available for Gmail accounts as they don't support subfolders [23]), additional options are shown to determine the structure of the "Archives" folder:

  • Choose from a single (flat) arrangement, grouping by year (default), or by year and month.
  • The checkbox allows you to retain the structure of the original folder in the "Archives" folder, which are arranged underneath the optional year and month folders.
  • The folder tree shows an example for the resulting folder structure and is not derived from any of your own folders.

In addition to the per-account settings, you can set the defaults for these preferences in the Config Editor. Any account which doesn't have specific settings will inherit from those preferences:

  • mail.identity.default.archive_enabled
  • mail.identity.default.archive_granularity
  • mail.identity.default.archive_keep_folder_structure

Auto compacting by default

related article: Compacting folders#Automatically

The defaults for compacting folders automatically have been changed [24]. It is now enabled by default and the threshold specified in MB rather than KB with a new default of 20 MB (ranging 1-2048 MB). These settings can be changed in the Advanced → Network & Disk Space options.

Attachments and inline images

Attachment sizes

There are several improvements and changes to the attachment panes in both the message viewer and the composition window. The sizes of individual attachments as well as the sum of all attachments are now shown when composing [25] or viewing [26] a message. This helps to estimate download times and to avoid messages bouncing back due to the server's size limit being exceeded.

Note: The sizes are for the raw attachments, thus not considering the overhead of encoding. As a rule of thumb, for each 10 MB message size allowed by the provider you can have 7.3 MB of raw attachment (assuming base64 encoding and 76 characters per line).

Attachment pane redesign


Another major change in the message viewer is the attachment pane, which is collapsed when opening a message and features a new attachment bar [27]:

  • By default, only the number of attachments, their total size, and an action button are shown (which contains the same actions as provided in the attachment-pane context menu).
  • For a single attachment, you can open it right away by clicking on the attachment name.
  • For multiple attachments, you have to use the twisty to the left to see them in detail.
  • The opened view corresponds to the attachment pane in previous versions, including the context menus.
  • Note that the action button and the context menu contain "Open" and "Open All" items now.

It has been criticized that the attachment pane now always appears collapsed without an option to open it expanded by default [28]. While an add-on is provided to work around this limitation and allows hiding the attachment bar entirely [29], it is also possible to modify the default behavior with a couple of userChrome.css entries.

As a compromise between showing it collapsed (thus not providing direct access to the attachments even if only a few are provided) and always expanding it by default (thus potentially using up a lot of space when the message has lots of attachments), the following code shows only first row of attachments when opening, then allows opening in full with the toggle [30]:

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

As another quick workaround, the following code always opens the attachment pane completely, in which case the twisty is redundant and thus removed:

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

#attachmentToggle {
  display: none !important;

Note: This variant needs to be extended for Thunderbird 8.0 and later. Either version is beneficial if you receive only a small number (but more than one) of attachments on a regular basis.

Images and links in HTML messages

In previous versions, View → Message Body As → Plain Text would arrange any images contained in the message and usually to be displayed inline in the attachment pane. This allowed recognizing easily when images were included in the message even in plain-text mode, thus a hint to switch to either Simple HTML or Original HTML modes. It also allowed for a "Save All" on included images. This feature unfortunately is no longer available in 5.0, images as part of the message body are only visible and accessible in the Simple HTML or Original HTML modes [31]. Note: A workaround will be provided in Thunderbird 8.0.

When composing a message, images pasted into the message body do no longer produce a temporary "moz-screenshot.{png,jpg}" file, instead the image is encoded in HTML itself [32]. The same mechanism is now also used when an image is dragged-and-dropped from a file into the message body, creating a snapshot of the image rather than just a reference to the file [33]. Be careful when using Insert → HTML with a portion highlighted that contains such an image, given that the entire image is encoded in HTML and may substantially delay opening of the "Insert HTML" dialog.

As a side effect, images inserted by copy-pasting or drag-and-drop now have a randomized file name [34]. When saving an image using its right-click menu, you will see an arbitrary string of characters followed by the ".png" or ".jpg" ending representing the file type. Either save it with the random name or highlight the part before the file extension and replace it with something useful. Make sure to retain the file extension so that it is properly recognized by the operating system.

When opening the Link Properties dialog with Insert → Link, note that copy-pasting a URL (e.g., from a browser) into the Link Location field using right-click → Paste does no longer work [35]. Instead, click into the Link Location field to focus it, then use the Ctrl+V keyboard shortcut to paste the web address. Note: Fixed in Thunderbird 6.0.

Moving account and mail tabs

All but the left-most tab now can be moved to a different location or opened as a new window [36]. Use the left mouse button to grab the tab you want to move, then drag it to its new position. Note the little down arrow which indicates where the tab will be inserted once you release the mouse button.

Existing tabs can also be detached to open as a new window. Either use the mouse to drag the tab you want to move over your desktop, or right-click on the tab and select "Move to New Window" from the menu. For message tabs, this is not equivalent to "Open Message in a New Window" as a full 3-pane window is currently opened rather than a stand-alone message viewer [37].

Software updates

Update options in the Advanced → Update preferences haven't changed. However, there is no longer a "Check for updates" menu item in the Help menu if you opted for manual updates. Instead, use Help → About and find the button to check for updates there. Note that clicking the button will download and install the update if one is provided, there is no longer an option to decline an offered update in a second confirmation dialog.

It is not clear at the time of writing if Thunderbird will employ "silent" updates which work in the background and are transparent to the user. Such a system is envisioned in the Firefox development document [38]

Advanced options

Signature delimiter

A long-standing request to make the "-- " (dash, dash, space) signature delimiter optional has been addressed by introducing a hidden preference [39]. To switch it off for all identities of your accounts, change mail.identity.default.suppress_signature_separator to "true", or look up the respective id# and create a new boolean preference for a specific identity.

Note that removing the signature separator makes it a part of the message you compose. Thus, similar to the already existing issue when the signature is placed below your reply but above the quote, signatures will no longer be removed when changing identities or replying [40].

As an interesting twist, the new preference provides a way to always add the signature separator, even with top replies and signature placed above the quote. Set the preference to "true", but then add explicit "-- " separators to your signatures. While this makes it consistent, quotes are now considered part of your signature and removed when replied to them.


Display of large message/attachment sizes

For both total message and attachment sizes, only values less than 1.0 MB are shown in KB, then the size is presented in MB [41]. This has the advantage that you don't have to calculate any more how many KB are a MB (1024 would be the answer), but makes it harder to spot large messages or attachments in the list.

To add a special marker to large sizes, you can add a file custom-strings.txt to the "chrome" folder of your installation directory with the following content:

chrome%3A//messenger/locale/***%.*f MB

This will add *** in front of messages for which the MB notation is chosen. You can reduce this to just a single * or any other string that is easily recognized by replacing the part between the = and the % in that string.

New add-ons manager

Thunderbird 5.0 now has the same Add-ons Manager which you may be familiar with already if you are using Firefox 4.0, opening in a content tab rather than in a separate dialog. The individual pages have been redesigned, but the basic functionality of each page remains the same.

The "Themes" tab is now labeled "Appearance".

In the "Get Add-ons" tab, recommendations are made based on your existing add-ons if you have three or more installed already. This involves sending information on your installed add-ons to Mozilla's web site in order to make those recommendations. There is a hidden preference extensions.getAddons.cache.enabled which you can set to "false" to avoid exposing that list to the add-ons site [42]. Also see Privacy considerations below for further information on communication between Thunderbird and Mozilla sites.

There have been reports of flickering buttons and other items of the Add-ons Manager on certain platforms [43], [44]. Resizing the window or switching tabs usually resolves those for the session, if any specific hardware is still affected by this problem.

Custom bindings

By default, the files stored in an extension's XPI file are no longer unpacked but just retained in a single archive file located in your profile. If you are using the User Chrome (chrome.xpi) extension to define custom code for bindings in a file userChrome.xml of your chrome folder, you will need to set extensions.alwaysUnpack to "true" prior to its installation. This is necessary to avoid restricting the add-on to the scope of its XPI file [45] and may also apply to other extensions which establish a chrome context outside of the extension itself.

Troubleshooting information

To improve support, Help → Troubleshooting Information opens a new content tab with detailed information on the build and platform you are using as well as any modified preference settings. Use this when being asked for such information in support forums, be careful though when using the "E-mail this information" function or when copy-pasting the entire information using the button provided as it may contain too much information for that specific case. It also contains information on server names which you may or may not want to disclose. No account credentials are contained in that report.

Privacy considerations

Scam warning

The implementation of the scam feature remains incomplete [46]. It is based on a fixed set of rules which are triggered when an HTML message contains links with either a numerical IP address or where the text over the link suggests a different target than the actual link underneath. Unfortunately, many newspaper-style messages and notices follow the latter pattern, usually to keep track of clicked links in such messages to get some statistics how frequently such a link was clicked. There is currently no way to white-list such links [47], and no service similar to the Google-based phishing list Firefox is using has been established for Thunderbird [48].


A request to disable the feature by default for the time being has thus far been denied [49], but as a workaround it has been made more apparent that the feature can be switched off. The scam warning now comes with a direct link which will disable the feature for this and all other messages [50], thus it's easier to find when too many false positives are reported. To reactivate the scam warnings, check the respective box in the Security → E-mail Scams options.

Note that, even though Thunderbird does not have an agreement yet with a phishing-list provider, right-clicking on a suspicious link in a message you received allows you to report that link as such to a provider [51].

Phoning home

Thunderbird may connect to certain sites, e.g., to pick up blocklist updates or changes in meta information for add-ons. There are however also cases where information about your specific installation is sent to a Mozilla site. The official Mozilla KB provides a list of connections initiated by Thunderbird [52].

Here some more information on specific preferences and their roles:

  • extensions.blocklist.enabled - leave this at "true" as Thunderbird only retrieves this list without sending any data on your local setup to the site.
  • extensions.getAddons.cache.enabled - this preference was already mentioned with respect to add-on recommendations. A list of your installed extension is not only sent to Mozilla when you explicitly open the Add-ons Manager, but also periodically to verify if any information on installed add-ons is outdated [53]. Setting this preference to "false" prevents this communication but will still allow for automated add-on updates if those are enabled in the Advanced → Update preferences.
  • extensions.getAddons.get.url - this is the URL used for the Get Add-ons page and has been supplemented with timing information which is sent during meta-data checks [54]. There is no identifying information, they are merely intended to document performance. Remove the time-related components between the & to avoid sending these parameters.
  • mail.instrumentation.askUser - initially it was intended to provide for some "instrumentation" dialog that the user will be presented with after account setup to provide performance and satisfaction feedback to the developers [55]. However, only the backend was implemented, and only for account setup. At this time it is not known which other parameters are intended for this opt-in feedback, and due to the lack of a UI it shouldn't be used for now, but you can set this preference to "false" to avoid being bothered when it is.
  • mail.instrumentation.postUrl - if you are paranoid about the instrumentation part, set this to http://localhost/ which redirects any requests of that type to your own computer (and thus won't find anything, unless you are running a web server locally).

A point of concern regarding the instrumentation code is that it would send a hash of your e-mail address if used in a future version [56]. While this hash likely wouldn't allow to derive your actual e-mail address, it could be used as a unique identifier to match parameters across different installations.

See also