Mozilla Release Notes

Changed

• Quick filter responsiveness has been improved
• ExtensionSettings policy installs add-ons from update_url when install_url not set

Fixed

• Copy Link Location only copied detached attachment filenames instead of full paths
• Thunderbird could crash while performing a Body search
• Troubleshooting falsely reported crash reports were not configured when available
• Right-clicking inline images zoomed them instead of opening the context menu
• Switching to Unified Folders could leave All Folders enabled and not change view
• Archived Inbox folders ignored localized names and appeared as "INBOX"
• OpenPGP key management had unlocking, handle leak, and protection state issues
• OpenPGP backup password text could not be copied and context menu was transparent
• Quick Filter failed to match accented names when searching without accents
• Holding Ctrl+Enter could unintentionally confirm the send prompt and send duplicates
• Plain-text inline forwards omitted signatures placed below the quote
• Remote content exceptions without a scheme only applied to HTTP, not HTTPS
• Remote content exceptions incorrectly allowed wildcard hostnames like *.example.com
• Saved CalDAV/CardDAV credentials could be forgotten after restarting Thunderbird
• CardDAV setup failed without prompting for a password
• CardDAV address book sync failed to fetch newly added contacts
• CardDAV updates could corrupt vCard REV timestamps
• CardDAV discovery could fail on valid multi-status responses with mixed status codes
• SMTP Kerberos authentication failed on Linux with STARTTLS
• POP accounts repeatedly showed connection errors when Thunderbird started offline
• Matrix SSO with Save Token disabled reopened the login flow indefinitely
• RSS filtering could lose tags and stall processing of later feed items
• CalDAV password prompts did not identify the username or calendar
• Calendar event edits could fail with localization error in the event dialog
• Updated calendar credentials were not saved from the authentication prompt

Visual and UX improvements

Security fixes

As always, you’re encouraged to tell us what you think, ask for help, or file a bug in Bugzilla

New

You can now fill in forms faster in Smart Window. When clicking into a form field or selecting Fill from sources, Smart Window will now suggest data to use based on your relevant open tabs and saved autofill data.

This feature is part of a progressive roll out.

Firefox now creates more accessible PDFs when saving a page as PDF, and when printing on Linux and macOS. This also fixes a variety of PDF rendering issues, such as missing math symbols.

Firefox now supports the JPEG XL image format, which generally has better compression than WebP, JPEG, PNG, and GIF.

New Tab now keeps a library of custom wallpapers under Your images, rather than only the most recent one.

Firefox's translations feature now supports the following languages:

• Albanian
• Belarusian
• Filipino

Fixed

Fixed website icons (favicons) in address bar results blending into the highlight color when selecting a result with the keyboard on Ubuntu's default theme.

Fixed a crash that could occur while Firefox loaded website icons (favicons).

Fixed the first letter of each search engine's name being underlined in the Unified Search Button menu in the address bar on Windows and Linux, which could cause conflicting keyboard shortcuts.

Fixed menus such as List all tabs, Settings, and Unified Search being hard to read with a Windows High Contrast theme. Menu background and text colors now follow the Background and Text colors chosen for a custom contrast theme in Windows Settings.

Various security fixes.

Changed

Firefox no longer rounds scroll positions to whole screen pixels. Scrolling is now smoother and more precise, especially on high-resolution displays or when a page is zoomed.

Enterprise

For Firefox Enterprise updates and fixes, see the Firefox Enterprise release notes. For policy changes, see the Firefox admin docs changelog.

Developer

Developer Information

Fixed an issue where the Network Monitor could miss WebSocket messages if they arrived immediately after a connection was established.

Web Platform

Firefox now supports typed arithmetic in CSS calc(), allowing units to be multiplied and divided within math functions.

Added support for the navigate option for the Notification constructor and ServiceWorkerRegistration.showNotification(), which specifies a URL to navigate to when the notification is clicked.

The WebAuthn conditional UI is now shown on input elements with an autocomplete="webauthn" attribute. Previously, it was only shown when the attribute included another autofill field value, such as autocomplete="username webauthn". (Learn more)

Firefox now supports the cache value for PerformanceResourceTiming.deliveryType, allowing websites to identify resources served from the HTTP cache.

The WebGL extension EXT_polygon_offset_clamp is now available on compatible devices.

Community Contributions

With the release of Firefox 158, we are pleased to welcome the developers who contributed their first code change to Firefox in this release, 20 of whom were brand new volunteers! Please join us in thanking each of these diligent and enthusiastic individuals, and take a look at their contributions:

• :cat: 2071142
• Adham: 1985986
• Anand Balaji: 2072754
• Calvin Lei-Cramer: 1975584
• Collins Kubu: 2069323
• Daniel mungai chege: 2072565
• f3tch [:f3tchcodes]: 1492357, 1917288, 1957843, 2068045, 2070577
• foued: 2070398
• harry75369: 2000420, 2006226, 2071759
• HojunCho: 2066829
• ianlewisuk1: 2072737
• Jakub Stasiak [:jstasiak]: 1719394
• Lavindeep: 2069768
• Ole Baumann [:darkintaqt]: 2070873
• Rehan: 1688932
• Ruslan Semchenko: 105707, 2041999, 2071549
• Sho Sakuma: 2072520
• Thomas Nibler [:tnibler]: 2071644, 2072008, 2072750
• Vir Patel: 1865119, 2073619
• Yeet: 1973441

Version 157.0, first offered to Release channel users on September 29, 2026

New

Firefox's biggest visual refresh in years is now available, with a modernized look across the browser toolbars, sidebar, menus and individual features, built with our updated design system. It also includes:

• New built-in themes with light and dark versions, to personalize the look of Firefox in one click.
• A new compact mode that reduces toolbar and tab spacing to leave more room for web content, useful on smaller screens and in split-screen layouts.

WebRTC video calls can now use hardware AV1 decoding on devices that support it, instead of always decoding AV1 video in software.

Firefox now shows a warning in the site information panel (the shield icon in the address bar) and in Settings when it has been set up to record its encryption keys, which could let other software on the computer read encrypted web traffic.

Firefox Suggest now offers suggestions in the address bar in Austria, Belgium, Czech Republic, Denmark, Finland, Hungary, Ireland, Luxembourg, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, and Switzerland. They can be controlled in the Firefox Suggest settings. Learn more.

Fixed

Fixed video from phones and tablets appearing sideways or upside down in WebRTC calls.

Fixed the address bar searching for the typed text instead of opening the selected suggestion when a page was still loading, such as shortly after Firefox started.

Fixed some HDR videos encoded in 8-bit color formats looking dull and gray on Windows instead of displaying in HDR.

Improved audio and video synchronization when repeatedly changing the playback speed of videos, for example on YouTube.

Fixed the Vertical Tabs sidebar not reappearing when the cursor moves to the edge of the screen in full screen mode.

Fixed an issue on Windows where making a video full screen would leave the Windows taskbar showing over the video.

Various security fixes.

Changed

Pressing Tab now moves focus straight to the text field of the address bar and search bar instead of stopping on the search engine button first. The button can still be reached with Shift+Tab.

Amazon is no longer included as a built-in search engine. It can still be added as a custom search engine in the search settings. Learn more.

The updated sidebar is now enabled for everyone. Anyone still using the previous sidebar will keep a similar layout, with the panel switcher at the top of the sidebar. Additionally, the “Show sidebar” option has been removed from Settings.

While we continue to refine the new design, the previous sidebar version can still be restored by setting sidebar.revamp to false in about:config. This also turns off vertical tabs. The preference will remain available until the end of 2027.

Web page alert(), confirm(), and prompt() dialogs, the color and date pickers, and form autocomplete drop-downs now match the page's light or dark color scheme.

Enterprise

You can find information about policy updates and enterprise-specific bug fixes in the Firefox for Enterprise 157 Release Notes.

Developer

Developer Information

Web Platform

Firefox now supports the at-rule() function for @supports. This allows authors to detect browser support for specific at-rules, such as @supports at-rule(@scope).

Firefox now supports the chain value for the CSS overscroll-behavior property.

Community Contributions

With the release of Firefox 157, we are pleased to welcome the developers who contributed their first code change to Firefox in this release, 21 of whom were brand new volunteers! Please join us in thanking each of these diligent and enthusiastic individuals, and take a look at their contributions:

• Alexander Gankov: 2033184
• Amadi: 2053549, 2053553, 2065302, 2066478
• Andrew: 2031465
• Caleb Pickard: 2058970
• David Torcivia: 2057758
• dchen705: 2065655
• Ekerin Agboola: 2064541
• Giddeon Card: 2067328
• gustavokrm: 2051536
• Hanzala Sohrab: 2068111
• Ivan Smagin: 2061540
• Jieke Jiang: 2067179
• Nazeer Ahmed Shaikh: 1703780, 2064544
• Noah Varghese: 1625924, 2021799
• perdomojuan755: 2069230
• Raúl: 2066877
• Rév O'Conner: 1594489
• Samuel Mbabhazi: 2054228
• sfshah: 2004273, 2067302
• Valerie Racine (:v-racine): 1849963
• Xiaosen Zhuang: 2069280

Changed

RNP command-line utilities are no longer included with Thunderbird

Thundermail built-in add-on updated to v2.0.16

Fixed

Ctrl+Shift+K could fail to open the Quick Filter UI

Nested S/MIME signed parts could fail to render

Thunderbird could hang when waiting for IMAP server greeting during account setup

Gmail OAuth2 authentication could intermittently fail on Windows

AppUpdatePin policy did not prevent Thunderbird from updating beyond pinned version

"What's New?" linked to Release channel notes instead of ESR release notes

Security fixes

As always, you’re encouraged to tell us what you think, ask for help, or file a bug in Bugzilla

What’s New

• Enterprise policy DisableChat disables Thunderbird Chat functionality
• Enterprise policy DisableFileLink disables Thunderbird FileLink functionality

Changed

• Preference mailnews.headers.minNumHeaders has been removed
• Allow viewing remote content in OpenPGP messages encrypted with integrity protection
• RNP command-line utilities are no longer included with Thunderbird
• IMAP/POP manual config port field is now optional
• Thundermail built-in add-on updated to v2.0.16

Fixed

• Ctrl+Shift+K could fail to open the Quick Filter UI
• Message list could show the wrong sender for messages
• Status bar could remain active and cause 100% CPU usage after activity ended
• OpenPGP discovery failed to find replacement keys after a key was revoked
• Valid RSA OpenPGP keys could be rejected, preventing encryption
• Sent messages could silently fail to save to the IMAP Sent folder
• Sending message did not fail gracefully with malformed references header
• Thunderbird could hang when waiting for IMAP server greeting during account setup
• Account Hub account creation could fail with malformed URI
• Custom OAuth Endpoint Host incorrectly required a full URL instead of a domain
• Message filters could falsely match when evaluating search term failures
• CardDAV address books could fail to sync when no password prompt was needed
• Yahoo emails appeared blank with MIME handlers disabled via mailnews.display.disallow_mime_handlers
• Pending moves within the same IMAP account could make messages disappear
• Inline images could disappear after editing and resaving drafts
• SMTP OAuth2 failed when large access token exceeded command line length limit
• Gmail OAuth2 authentication could intermittently fail on Windows
• Exchange NTLM authentication failed when updated passwords were not saved
• SMTP AUTH LOGIN could fail after username challenges and close the connection
• AppUpdatePin policy did not prevent Thunderbird from updating beyond pinned version
• Recurring events could appear after their configured end date
• CalDAV task body could remain outdated after syncing changes from another client
• CalDAV invitations could fail when accepted before the calendar synced

Visual and UX improvements

Security fixes

As always, you’re encouraged to tell us what you think, ask for help, or file a bug in Bugzilla

Version 156.0.1, first offered to Release channel users on September 22, 2026

Fixed

• Fixed the NVDA screen reader not announcing address bar buttons when the mouse pointer moves over them. (Bug 2069276)
• Fixed elements inside a link not showing their CSS :active styles while being clicked. (Bug 2067272)
• Fixed Firefox becoming unresponsive on some pages that use CSS anchor positioning. (Bug 2070171)
• Fixed Firefox windows on macOS 27 immediately returning to maximized after being restored by double-clicking the title bar. (Bug 2066632)
• Fixed Firefox leaking system handles on Windows as content processes were started and stopped. (Bug 2069644)

Changed

• Pressing Tab now moves focus straight to the text field of the address bar and search bar instead of stopping on the search engine button first. The button can still be reached with Shift+Tab.

Reference link to 156.0 release notes.

Fixed

Detached attachment links were truncated when folder path contained &
Save All, Detach All, and Delete All failed after deleting one attachment
Blank 1970-dated messages could appear from incomplete message file copies
Forwarded messages could display incorrect encoding
Manual Get Messages failed after startup until toggling offline mode
Thunderbird could crash on shutdown while waiting for OAuth2 password entry

Security fixes

As always, you’re encouraged to tell us what you think, ask for help, or file a bug in Bugzilla

New

• Firefox on macOS can now be set to open automatically when the computer starts up, from the Startup section of Settings.
• Localized Wikipedia and occasional sponsored suggestions in the address bar are now available in France, Germany, and Italy. These suggestions can be turned off in Firefox Suggest settings.

Fixed

• Fixed an issue where dragging an image to a new position in a rich-text editor could replace it with a long line of text instead of moving it.
• Fixed high-sample-rate FLAC audio in MP4 failing to play on sites such as Bilibili.
• Fixed subtitles not appearing in the Picture-in-Picture window when they are turned on in the video player after the window has already opened.
• Fixed bookmarks moving out of their folder when the folder and the bookmarks inside it were selected and dragged together in the Bookmarks sidebar.
• Fixed the find bar becoming permanently unavailable in a tab after reversing the panes in Split View.
• Fixed some sites failing to load when DNS over HTTPS is enabled and the site does not support HTTPS.
• Fixed Firefox losing all network connectivity for some users with the built-in VPN enabled.
• Fixed an issue on Windows where Firefox could block an auto-hiding taskbar from showing.
• Various security fixes.

Changed

• Firefox's built-in PDF viewer now starts up to 45% faster.
• Improved memory and CPU usage when Firefox displays large JPEG images scaled down to fit a page.
• On Windows devices with ARM64 processors, WebRTC video calls may now use hardware H264 decoding instead of falling back to software.

Enterprise

• You can find information about policy updates and enterprise-specific bug fixes in the Firefox for Enterprise 156 Release Notes.

Developer

• Developer Information

Web Platform

• text-box-trim now uses the font metrics of a ::first-line pseudo-element when one applies, matching other browsers and the specification.

Community Contributions

With the release of Firefox 156, we are pleased to welcome the developers who contributed their first code change to Firefox in this release, 10 of whom were brand new volunteers! Please join us in thanking each of these diligent and enthusiastic individuals, and take a look at their contributions:

• Aaron Ma: 2063818
• Dominik Bay [:eimann]: 2066736
• ExplodingJoysticks: 1728637, 1890400, 1910664, 1928343, 1944206, 2000658, 2003000, 2059911, 2061541
• Gopalarathnam Venkatesan: 2003172, 2042426, 2062096, 2062952, 2062989
• Hugo Osvaldo Barrera: 2063808
• Kana: 2062133
• Kerissa Grubb: 2042422
• Louis-Philippe Manette: 2062972, 2063867
• Seunghyun An: 2063033
• William McDonald: 1034964

What’s New

• OpenPGP key properties can print debug information to the Error Console
• External browser login flow enabled for Yandex
• Custom OAuth support for issuer ID and client secret field for IMAP and POP3
• Custom OAuth support for POP3
• Enterprise policy DisableUpdateSettings prevents users from changing update settings
• Enterprise policy DisableDataCollectionSettings prevents users from changing data collection setting
• Enterprise policy DisableMessageForwardingFilters prevents message filters from automatically forwarding messages

Changed

• Preference mail.offer_experimental_features renamed to mail.experimental_features_settings.enabled
• Thundermail built-in add-on updated to v2.0.11

Fixed

• Detached attachment links were truncated when folder path contained &
• Opening a PDF attachment in a tab displayed empty tab
• POP3 folders with names over 55 characters could become duplicated after upgrading
• Folders with invalid filename characters could show hashed names if cache was lost
• Save All, Detach All, and Delete All failed after deleting one attachment
• Renaming folders could reset folder settings
• Subscribing an IMAP folder and subfolder together failed to subscribe the subfolder
• Some newly fetched POP messages were not marked with new star after startup
• Sorting after deleting the only child message removed the parent from view
• OpenPGP signing failed with external GnuPG when the primary key could not sign
• Remote content could load in encrypted messages opened from files
• Sent message with expired S/MIME certificate wrongly showed untrusted CA warning
• PDF attachments from compose windows could wrongly be detected as HTML
• Saving unconfirmed recipients could create invalid address pills with >>
• External browser OAuth failed when a browser preconnection closed first
• Users could not set up custom OAuth for Exchange accounts
• Pressing Enter on Windows system tray icon did not restore Thunderbird window
• Inline attachments incorrectly changed the message channel content type
• Message loading was slow while discovering large numbers of IMAP folders
• SMTP authentication failed when usernames contained non-ASCII characters
• Unsupported EWS archive folder prevented all mailbox folders from syncing
• Manual Get Messages failed after startup until toggling offline mode
• Case differences in CalDAV email addresses caused duplicate invitations
• Accepted CalDAV invitations could be saved to the wrong calendar

Visual and UX improvements

Security fixes

As always, you’re encouraged to tell us what you think, ask for help, or file a bug in Bugzilla

Version 155.0.1, first offered to Release channel users on September 4, 2026

Fixed

• Fixed Firefox becoming unresponsive on some pages that use CSS blur and backdrop filters together. (Bug 2068836)
• Fixed the sidebar not reappearing after restarting Firefox when the "Hide tabs and sidebar" option was turned on. (Bug 2065431)
• Fixed some profile icons not being displayed in the account and application menus. (Bug 2064729, Bug 2067734)
• Fixed the current device being listed among connected devices in the account menu. (Bug 2059763)

Reference link to 155.0 release notes.

Unresolved

Standard dynamic range (SDR) video in some formats can appear washed out on macOS. The issue is under investigation and a fix will ship in a future release. (Bug 2068961)