Mozilla ships Firefox 153 ESR as Thunderbird 153 piles on fixes

Mozilla released Firefox 153 on Tuesday as its new Extended Support Release, while MZLA followed with Thunderbird 153, an ESR release codenamed “Meadow.” The Firefox update matters most for organizations and users that standardize on ESR builds: Mozilla says Firefox 153 will receive security updates until sometime after the next ESR arrives in mid-2027.

The most notable Firefox change is a preview of Multi-Account Containers functionality built directly into the browser. Firefox has long supported separate profiles for isolating settings and credentials, but profiles can be cumbersome if a user wants multiple identities active at once. Containers address that use case more directly by keeping credentials separate by container, so the same site can be open in different tabs under different logins.

Mozilla is also adding platform-specific features. Firefox 153 for Android includes tab groups. In the United States, Firefox for iOS adds Quick Answers, a feature that uses on-device speech recognition, while Mozilla says the transcribed question is sent online to generate the answer.

Thunderbird gets an ESR with a long fix list

MZLA’s Thunderbird 153 is also an ESR release and replaces the prior “Eclipse” line with the “Meadow” codename. MZLA has not said much publicly about what the codename refers to, and release documentation appeared uneven at launch: the “New in Thunderbird Desktop” page had not been updated beyond Thunderbird 150, which shipped in April.

The Thunderbird 153 release notes are more substantive. MZLA lists 32 refinements, 15 changed items and 181 fixes. That is a large maintenance payload for an ESR build and suggests the release is less about a single headline feature than about stabilizing and cleaning up a broad mail client that now spans email, calendars, contacts, encryption and multiple account types.

MZLA says Thunderbird 153 includes improvements across folder behavior, notifications, OpenPGP encryption, OAuth login, address book export and PDF handling. The project has also dropped 32-bit Linux binaries, matching a move Mozilla previously made for Firefox after version 144.

Some naming and service-specific changes are visible to users. Thunderbird now uses “Spam” where it previously used “Junk.” The dedicated account setup option for Russia’s Odnoklassniki service has been removed, with users directed to configure the service through XMPP instead.

Account handling points toward Thunderbird Pro

Thunderbird 153 also updates several account-management flows tied to Thundermail, part of MZLA’s planned paid email service under the Thunderbird Pro brand. The service has not launched, and MZLA has not disclosed pricing, timing or expected uptake. The account wizard now includes a “Sign in with Thundermail” button, which is a visible sign that the commercial email effort is moving closer to availability.

The release also tweaks Thunderbird’s alternate folder views. The “Unread Folders” view is now better at suppressing folders that have no unread messages. “Unified Folders,” which groups multiple inboxes and account folder trees into a combined view, now supports account color-coding.

The timing adds an operating question for MZLA. Thunderbird has been tracking Firefox’s monthly release cadence since Thunderbird 138 in April 2025. Mozilla has decided to move Firefox to a fortnightly release schedule from September, but MZLA has not said whether Thunderbird will follow that pace.

This story draws on original reporting from The Register.