Thunderbird released ESR 153.4.0 and ESR 140.17.0 on September 30, 2026. Both releases include security fixes and remove RNP command-line utilities from the Thunderbird package. Version 153.4.0 also lists fixes for Quick Filter, S/MIME message rendering, IMAP account setup, Windows Gmail sign-in, the AppUpdatePin policy, and the “What’s New?” link. Version 140.17.0’s notes list security fixes rather than comparable functional fixes.
What changed in each Thunderbird ESR release?
| Release | Changes and fixes listed | Security advisory |
|---|---|---|
| Thunderbird ESR 153.4.0 | RNP command-line utilities removed; built-in Thundermail add-on updated to v2.0.16; six functional fixes listed in the release notes. | Mozilla Advisory 2026-103 |
| Thunderbird ESR 140.17.0 | RNP command-line utilities removed; release notes list security fixes. | Mozilla Advisory 2026-102 |
The releases are point updates on separate ESR branches, so the longer functional-fix list for 153.4.0 should not be read as a list of changes also made in 140.17.0.
As an Amazon Associate I earn from qualifying purchases.
What’s fixed in Thunderbird ESR 153.4.0?
The 153.4.0 release notes identify these functional and administration fixes:
Recommended Free Tools
- Quick Filter: Ctrl+Shift+K could fail to open the Quick Filter interface.
- S/MIME: Nested signed message parts could fail to render.
- IMAP setup: Thunderbird could hang while waiting for an IMAP server greeting during account setup.
- Gmail on Windows: OAuth2 authentication could fail intermittently.
- AppUpdatePin policy: The policy did not prevent updates beyond the pinned version.
- “What’s New?” link: The link opened Release-channel notes instead of the ESR notes.
The release also updates the built-in Thundermail add-on to v2.0.16. This is a bundled add-on update, not a new feature first introduced to Thunderbird as a whole by version 153.4.0.
What does Thunderbird ESR 140.17.0 include?
The 140.17.0 release notes list security fixes and the removal of RNP command-line utilities. They do not enumerate functional fixes comparable to the six listed for 153.4.0. For vulnerability details, consult Mozilla Advisory 2026-102, which corresponds to 140.17.0.
What does the security update mean?
Mozilla published a security advisory for each build on September 30, 2026: Advisory 2026-103 for 153.4 and Advisory 2026-102 for 140.17. Mozilla classifies the overall impact of each advisory as high, while individual flaws have their own impact ratings. The advisory for 140.17, for example, describes issues involving browser-engine memory safety, sandboxing, networking and privileges, as well as a heap-buffer-overflow scenario involving an email at least 2 GB in size.
Mozilla says that, in general, the listed flaws cannot be exploited through Thunderbird email because scripting is disabled when reading mail, but they may pose risks in browser or browser-like contexts. That qualification is about the stated threat context; it does not mean the releases are risk-free or that every flaw has the same severity.
Quick wins for a faster PC:
Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Which operating systems does 140.17.0 support?
The 140.17.0 release notes state these minimum requirements:
- Windows 10 or later
- macOS 10.15 or later
- Linux GTK+ 3.14 or higher
The available 153.4.0 release-note information does not establish its equivalent minimum requirements, so these 140.17.0 requirements should not be assumed to apply to that branch.
Why a point release matters even without a long fix list
Mozilla Support describes ESR point releases as containing security upgrades and stability fixes. That helps explain why an update can matter even when its notes do not advertise many user-facing changes. Thunderbird 153 is the “Meadow” ESR announced in July 2026, built on 140 “Eclipse” with improvements from the monthly release channel. Its redesigned Account Hub and native Microsoft Exchange support are version-level features, not new features introduced by point release 153.4.0.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
