Betterbird Blog

We've shipped Betterbird 153.2.0esr-bb8 today. Please refer to the Release Notes for full details.

In this release, a few issues were fixed for Linux users:

• For some users, the system integration dialogue came up on every start. This should be fixed now.
• Due to the switch to a newer version of the library for Linux system tray support in 153.1.0-bb7, support for the Mate desktop had been lost. This was re-implemented now. Mate doesn't support the StatusNotifierItem (SNI) D-Bus protocol, hence we implemented a fallback to GtkStatusIcon. Desktops with don't support SNI can now be listed in the new preference mail.systemTrayNoSniSupport. On the Cinnamon desktop, the XApp Status applet for SNI support is generally installed, so the system tray icon works. If it's not present, x-cinnamon can be added to the preference. See our expert tips for details.
• Launching Betterbird again while an instance is already running and minimised to the system tray, will now restore the last main window. This matches the behaviour on Windows.

All platforms benefit from the following fixes:

The checkbox for matching display names and nicknames from the address book in a Quick Filter search didn't work. This was due to some changes in the Mozilla platform between versions 140 and 153 and has been corrected.

Some users got confused with respect to the location of folders for templates and archives, as their location wasn't correctly reflected in the UI in the Account Manager. As a consequence, Reply with Template was sometimes not available in the Filter Editor. Now the settings displayed in the Account Manager are accurate, also when IMAP namespaces are used, that is, all folders are, for example, located in an INBOX folder.

Lastly, more restrictive security settings in the Mozilla platform has malfunction of a few WebExtension Experiment add-ons as a consequence. New versions of popular add-ons like Lightning Calendar Tabs, ThunderHTMLedit and Sender Frequency have been made available and should be updated (semi-)automatically.

Noteworthy other affected add-ons: tbkeys-lite was updated on 31st August 2026 after receiving a hint from us, ImportExportTools NG and PrintingTools NG are not working at time of writing (2nd September 2026). However, the author has already submitted fixed versions to ATN, but they haven't been reviewed and released yet.

Since publishing 153.1.0esr-bb7 two days ago, we received a few support queries. So here are some notes addressing these concerns:

The Thunderbird folks renamed Junk to Spam throughout the product. There is no way going back.

The localisation of IMAP special folders (Inbox, Drafts, Templates, Sent, Archives, Outbox) has changed, they are now all localised and the original folder names on the server are ignored. To use the original server folder names set preference mail.useLocalizedFolderNames to false.

Special folders can no longer be renamed or deleted. In case of doubled-up folders, check the account configuration to see where Draft, Spam, etc. folders are referenced and make sure the desired folder is used. In cases which resist, the add-on FolderFlags can be used to clear folder flags and make folders deleteable.

There have also been reports of inaccessible IMAP folders or re-download of messages:

This is related to IMAP folder which use -1 (or -2 or higher) as suffix in their file names on disk.

This has been addressed in build 2, which is now available.

Finally, if as a Linux user you notice a thunderbird directory in your home directory, that's due to this upstream bug which we will fix in the next release.

We've shipped Betterbird 153.1.0esr-bb7 today. Please refer to the Release Notes for full details.

As announced yesterday, we're retiring the 140 series effective immediately.

Noteworthy changes between 153.0 and 153.1.0:

• On Linux, we upgraded the library that handles the system tray to the latest version. This fixes a related crash.
• Unlike in Thunderbird, dragging an image around in a compose window or to a different compose window works.
• We fixed a puzzling bug where new messages prematurely lost their indicator star.

As already mentioned in this article, the 153 series brings interesting new functionality, for example, the ability to store message (.eml) attachments directly in a folder, close to tray, Quick Look preview of attachments on Mac, and improvements to account colours.

A quick note about "close to tray" which in Thunderbird replaced "minimise to tray". Now users are asking for both to be available, which has always been the case in Betterbird.

We're also shipping 66 (!!) fixes the Thunderbird folks are not including their 153 ESR release (yet?). Apparently they want to lure users onto the release channel to get those fixes, but that's a roller coaster ride of regressions.

The Google Chrome team has decided to switch to a two-week release cycle as published in this article. Firefox and Thunderbird are following, see here and here. You can also check the Firefox/Thunderbird ESR release calendar here.

To reduce the workload of theoretically having to build eight binaries during the 140-to-153 overlap period, that is, Windows, Linux, Mac Intel and Silicon, we decided the following:

• 140.13.0-bb25 shipped on 21st July 2026 will be the last release in the 140 series. End-of-life for the 140 series will be reached with the release of 153.1.0-bb7.
• 153.1.0-bb7 shipping on 18th or 19th August 2026 will become the official release for all platforms.

The article picture shows the effects of two recent regressions in Thunderbird 153.0.2 (ESR).

The left part shows what happens when trying to drag a message or message attachment to the desktop or a folder: Unspecified error. This is tracked in this ticket. The breakage was caused by the Mozilla team when fixing a security issue in Firefox 155; this fix was backported to Firefox 153.0.2 and also hit Thunderbird.

The right part shows what happens when dragging an image in a compose window to a different location or another compose window: The internal representation of the image is inserted as text. This is tracked in this ticket. The breakage was caused by the Mozilla team implementing changes to drag and drop for Firefox 151 in March 2026. Here QA has completely failed, since no one detected the breakage with affects both Firefox and Thunderbird since version 151 until the end of July 2026.

To understand what has happened, let's dive into how code for Firefox, Thunderbird and Betterbird is structured.

Firefox at version 153 consists of roughly 40 million lines of code. This includes code for the Firefox frontend (tab bar, address bar, bookmarks, and other Firefox-specific UI); Firefox mobile; the SpiderMonkey JavaScript engine; the DOM implementation; the layout and graphics pipeline covering CSS style resolution; the WebRender compositor, font rendering, and image decoding; the networking stack handling HTTP, DNS, and sockets; the NSS cryptography library providing TLS and certificate handling; the media engine for audio, video, and WebRTC; the XPCOM component model, which bridges JavaScript and C++ and provides cross-platform file I/O, threading, string handling, and process management; the widget layer that abstracts native windowing, event loops, clipboard, and drag-and-drop across Windows, macOS, and Linux; internationalisation; the shared toolkit providing preferences, add-on management, password storage, printing, downloads, and other cross-application services (Places, Find-in-page, Search engines, Autocomplete, Crash reporting, Telemetry (the latter two not being used in Betterbird)); and additionally the developer tools.

Of these 40 million lines, five million lines covering the Firefox frontend and Firefox mobile, are not shared by Thunderbird/Betterbird. Thus, these programs use 35 million lines of the so-called Mozilla platform code and two million lies of code of their own. Those two million lines cover the frontend and the backend with the following functionality: IMAP, POP3, Exchange and NNTP protocol implementations; the message database layer (including the legacy Mork format, the newer Gloda global-message-database and the future Panorama database); MIME parsing; message composition including HTML editing; the address book with LDAP and CardDAV; OpenPGP and S/MIME encryption; mail import/export; also included are Calendar (local calendars, CalDAV, invitations and scheduling, import/export) and Chat (IRC, XMPP, (defective) Matrix).

As mentioned above, the two regressions were caused by changes in the Mozilla platform code which is geared mostly towards Firefox. There was little chance to catch the first one since it was implemented for Firefox 155 at the end of July 2026, and was integrated into earlier branches, like the 153 release and ESR branches, almost immediately. Of course, an automated test would have caught it straight away, but despite touting their test suite, the Thunderbird test suite has many holes, also for very important functionality. There were more than four months to detect the second issue, but it went undetected until very recently.

Betterbird 153.0esr users are not affected by the first issues and we have published 153.0esr "build 7" with a fix for the second issue, well ahead of Thunderbird.

In general, at Betterbird, we patch both the Mozilla and the Thunderbird codebase, whereas the Thunderbird folks only manage their own code and rely on Mozilla staff for backporting fixes in the Mozilla platform code. This leads to delays in fixing bugs in the ESR version of up to one year.

When the Betterbird CEO was still in charge of Thunderbird releases until 2019, Thunderbird didn't rely completely on Mozilla staff for backports, it could independently fix bugs in the ESR version. These days, the Thunderbird folks either don't care or lost the ability.

Let's fill the summer hole/silly season with some content.

Two days ago we switched to Betterbird 153 for productive use. At first, everything looked good, but then we noticed a few regressions:

Our suggested userChrome.css had an issue, the "cute icons" didn't work any more: That got fixed and an update was published here.

Next we discovered an issue in ThunderHTMLedit. The Mozilla folks had tightened security by disallowing blob:system workers. That change snuck into Thunderbird/Betterbird beta 6. We adjusted the add-on accordingly and published version 3.6.6.

Finally we noticed that after pasting a screenshot into a composition, the caret ended up at the wrong location before the inserted image. Fortunately, someone had already reported the issue and Thunderbird's new star contributor flexed his AI muscle and provided a fix which we're currently evaluating.

Today we received this issue about Thunderbird's tags folder pane mode. This was half-implemented for Thunderbird's Supernova Kaboom version 115, and has been defective ever since the day of first shipping, as a few bugs ([1] [2] [3) show.

And while digging around Bugzilla, we found these pearls:

• Enable the defective tags mode by default: Abandoned by Thunderbird's own "Director, Desktop & Mobile Apps" - good one!
• Underline links: Looks like another Supernova victim. In Betterbird, setting the preference layout.css.always_underline_links will always underline links, also in message content.
• And as predicted in the article that states that Thunderbird development is driven by user complaints, those complaints about Thunderbird's poorly implemented account colours have now arrived. And the shonky design decision to not store the colours in preferences has come to bite.

What's happening at Betterbird during that the Germans call summer hole (Sommerloch), also called silly season in parts of the world?

The new ESR version 153 shipped about 10 days ago, and so far we had only little feedback, but all the feedback received was positive. Version 140.13.0-bb25 was also shipped around the same time.

We're constantly monitoring developments at Thunderbird, so a few days ago we shipped a build 2 for Betterbird 153.0esr-bb6. In that build, we shipped two minor corrections and additional upstream fixes.

While things are generally quieter, we've used the time to upgrade our macOS build machine to a Mac mini M4. This delivers faster builds, and keeps up with Apple's ever-changing Xcode requirements, and thus ensuring that Betterbird continues to build natively for Apple Silicon; it also allows a cross-compile for Intel Macs.

If you've been enjoying Betterbird, please tell a friend or colleague about it. And if you'd like to help keep the project going, consider sending a donation. Summer is traditionally a bit of a donation lull, so every contribution is especially appreciated. We don't run three or four yearly donation drives like the Thunderbird folks, only one in December.

We've shipped Betterbird 140.13.0esr-bb25 today. Please refer to the Release Notes for full details.

The Thunderbird had quite some trouble while building the release as mentioned in this earlier article. In fact, as they forgot to update the version number, their first successful build, not mentioning about eight failed builds, was built as 140.12.1/build2. Go figure. Three builds later they finally produced a correct build. However, the underlying Gecko version is already at 140.14.0, which could potentially affect some add-ons which are configured to only function to version 140.13.0.

Back to the Betterbird release. This release contains fixes some important bugs:

Zooming of images in links is back, after being removed from version 140.12.0, but this time controlled via preference mail.allow_zooming_image_links.

Spellcheck now works when the desired languages are stored in preference spellchecker.dictionary as a comma-separated list, for example: en-US,de,es-ES.

As mentioned, full details in the Release Notes.

Thunderbird 140.13.0 is due on 21st July 2026, but the Thunderbird folks have trouble building it. So, according to the motto that was coined when Thunderbird was run by volunteers, not 50+ staff turning over 10+ million USD, it will ship when ready.

We depend on a correct Thunderbird build, so Betterbird is also delayed. On the positive note, we managed to ship the next version on the 20th of July 2026.

Today we shipped the first version in the new 153 ESR series, Betterbird 153.0esr-bb6. At the moment, this is only available for Windows, in a few days, we'll offer binaries for for Linux and Mac. We'll see how stable this series turns out to be and when we will start promoting it as the new primary version superseding version 140.

We've analysed available bug fixes for Thunderbird carefully and we're shipping 32 fixes and features that the Thunderbird folks are so far not including in their 153 ESR series.

On top of the 32 extra fixes and features, Betterbird has another 220 improvements. We're happy to report that we just concluded an AI review of all patches and address the minor issues found before this release. Of course the current 140 ESR series will also be updated when 140.13.0 ships in the next few days, whenever the Thunderbird folks are ready.

Like always, everything is documented in the Release Notes.