Thunderbird Desktop
Version 159.0beta | Released October 14, 2026
Check out the notes below for this version of Thunderbird. As always, you’re encouraged to tell us what you think, ask for help, or file a bug in Bugzilla.
These notes apply to Thunderbird version 159 beta 2 released October 14, 2026.
System Requirements: Details
What’s New
new
Linux tray icons indicate unread mail and show its count in the tooltip
new
Graph calendars are auto-detected on new account creation
What’s Fixed
fixed
Non-ASCII IMAP tags could exceed server length limits and be rejected
fixed
Zoom Text Only option did not work in the View menu
fixed
Multiple messages were printed even after canceling the print dialog
fixed
Save All and Detach All failed for attachments with invalid filename paths
fixed
First Wrap Long Lines toggle did nothing in View Source
fixed
POP3 NTLM authentication failed because the password was sent incorrectly
fixed
Search Messages menu option was enabled but did not work for saved search folders
fixed
Quick Find shortcut (/) only worked after Ctrl+F was used once
fixed
Unicode email addresses could hide different Reply-To destinations
fixed
Newsgroups with UTF-8 names could display duplicate or incorrect messages
fixed
View > Folders did nothing in Calendar and Tasks tabs
fixed
Global search results did not display recipients in the To field
fixed
Forwarding malformed MIME messages could omit attachments
fixed
Retry and Save Locally failed after a sent-folder copy error
fixed
Closing an unmodified compose window prompted to save when using Body Text
fixed
MP4 attachments could be truncated when forwarding messages
fixed
Inline images disappeared when editing local or POP messages as new
fixed
EWS/Graph accounts could fail when outgoing server settings were incomplete
fixed
Account Hub Edit Configuration did nothing for Exchange and Graph accounts
fixed
First message filter condition could not be removed even when others existed
fixed
CardDAV address book sync stopped when the server rejected an invalid sync token
fixed
CardDAV passwords were not saved, causing repeated login prompts after restart
fixed
Malformed message database files could cause excessive CPU usage
fixed
IMAP namespace root folders were inaccessible due to duplicated folder names
fixed
Excessive Microsoft Graph requests caused throttling and delayed message display
fixed
SMTP addresses with line breaks could inject unintended commands
fixed
POP3 sessions remained active after canceling the password prompt
fixed
Remote content could load in news articles with missing message headers
fixed
RSS feeds could inject arbitrary Message-ID and References headers
fixed
Large ICS calendar files could exhaust memory and freeze Thunderbird
fixed
CalDAV calendars could stop syncing after a network error until restart
fixed
Yearly recurring events with multiple times per day only appeared at the first time
Fixed in beta 2
What’s Changed
changed
There are no Thunderbird changes requiring release notes in this release
