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Thunderbird Monthly Release 142 Recap

We’re back with another exciting Monthly Release recap! Thunderbird 142.0 brings a host of user-requested features and important bug fixes that make your email experience smoother and more reliable. From better folder management to smarter PDF handling, this release focuses on the details that matter most to your daily workflow.

A quick reminder – these updates are for users on our monthly Thunderbird Release channel. For our users still on the ESR (Extended Standard Release) channel, these updates won’t land until next July 2026. For more information on the differences between the channels and how to make the switch:

• Visit the Release download portal: Thunderbird Release Page.
• Explore detailed comparisons and migration guides.

Now let’s dive into what’s new in 142.0!

New Features:

Reset Manual Folder Sorting

Bug 1972710

Ever tweaked your folder order and wished you could start fresh? We hear you! Thunderbird 142 introduces a simple way to reset your folder sorting back to defaults. 

Benefits:

• The new Reset Folder Order option lets users right‑click an account in the Folder Pane to instantly clear any custom sorting. 
• Provides a quick clean slate and avoids manually dragging folders back to default positions.

Note: This feature resets sorting order but doesn’t restore folders that were moved inside different parent folders.

PDF Signatures and Attachment Handling

Bug 1970796

Thunderbird now lets you add visual signatures to PDF attachments opened inside the app. This update brings Thunderbird in line with modern PDF functionality, making it easier to handle contracts, forms, and other documents without leaving your inbox.

Benefits:

• Add a handwritten-style visual signature directly in Thunderbird.
• No need for external tools to sign simple PDF documents.
• Keeps everyday document handling faster and more convenient.

Custom OAuth Support for Add-on developers

Bug 1967370

New add-on API support for OAuth client registration now allows developers and organizations to add custom OAuth providers at runtime. Instead of requiring changes in Thunderbird’s core code, an add-on can handle the setup. 

Benefits:

• Supports custom OAuth providers through add-ons.
• Works with enterprise policies for organizational deployments.
• Simplifies integration with unique authentication systems.

Bug Fixes

Respect for “Do Not Disturb”

Bug 1876310

Your focus time is sacred, and Thunderbird now honors that across all operating systems.

Benefits:

• Native OS notifications now respect the “Do Not Disturb” setting of every operating system, including blocking calendar reminders and chat notification sounds.
• Delivers protected focus time and consistent behavior with other applications.

Improved Dark Reader Mode Toggle

Bug 1962931

Reading flow is now smoother when switching between light and dark message modes.  An issue was reported where toggling the setting in the message header would reset your scroll position and pull focus away from the message body. 

Benefits:

• Keep your scroll position in the message when switching between light and dark mode so you can continue reading without interruption.
• Retain focus on the message body for easier keyboard navigation.
• Reduce extra clicks and scrolling, making reading more seamless.

Message List Scrolling Fix

Bug 1968967

Unwanted scrolling of the message list that happened when returning to the Mail tab after opening a message is now a thing of the past. Instead of jumping to the top and slowly scrolling back down, the list now stays put.

Benefits:

• Keep your place in the message list when switching tabs.

PDF Attachments Reload Correctly on Startup

Bug 1970615

Thunderbird now correctly reloads PDF attachments that were left open in tabs when you restart the app. Previously, these tabs would fail to open and display an error, forcing you to reload them manually.

Benefits:

• Open PDF attachments are restored automatically on startup.
• No more error messages when resuming work.