2034823 - Update to tzdata2026b

Status: RESOLVED FIXED

(Core :: JavaScript: Internationalization API, task, P1)

Description

[André Bargull [:anba]]

Update to tzdata 2026b.

Important changes:

• British Columbia moved to permanent -07 on 2026-03-09

Release notes:

• https://lists.iana.org/hyperkitty/list/[e-mail]/thread/VX2Z3CBO6KHTYZNBBKFFWM7ZCI6TVCXP/

---

Important:
ICU4C doesn't yet support the new stdOffset/dstOffset annotations for meta zones (https://unicode-org.atlassian.net/browse/ICU-23338), which means the time zone display name is Pacific Daylight Time instead of simply Pacific Time:

js> Temporal.ZonedDateTime.from("2026-12-01[America/Vancouver]").toLocaleString("en-CA", {timeZoneName: "long"})
"2026-12-01, 12:00:00 a.m. Pacific Daylight Time"

Comment 1

[André Bargull [:anba]]

Attachment: Bug 2034823: Update to tzdata 2026b. r=#spidermonkey-reviewers!

Comment 2

[André Bargull [:anba]]

Attachment: Bug 2034823: Update to tzdata 2026b (ESR140). r=#spidermonkey-reviewers!

Backport for ESR140.

Includes the changes from tzdata releases 2025c and 2025a, which weren't
backported to ESR140.

Comment 3

[Ryan VanderMeulen [:RyanVM]]

Should we do this bump on ESR115 also?

Comment 4

[André Bargull [:anba]]

I wasn't planning to update for ESR115, because the changes for British Columbia only become visible in November, so after the (current) EOL date for ESR115. Also I don't know if Microsoft plans to distribute time zone updates for Windows 7 and unless they do, the system time will be off for users from BC anyway.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/38f7c06712ee
https://hg.mozilla.org/integration/autoland/rev/770065aec6b1
Update to tzdata 2026b. r=spidermonkey-reviewers,dminor

Comment 6

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/770065aec6b1

Comment 7

[Phabricator Automation]

firefox-beta Uplift Approval Request

• User impact if declined/Reason for urgency: Wrong time zone data when calling standard Date and Intl.DateTimeFormat methods.
• Code covered by automated testing?: yes
• Fix verified in Nightly?: yes
• Needs manual QE testing?: no
• Steps to reproduce for manual QE testing:
• Risk associated with taking this patch: low
• Explanation of risk level: It only updates time zone data files.
• String changes made/needed?: None
• Is Android affected?: yes

Comment 8

[André Bargull [:anba]]

Attachment: Bug 2034823: Update to tzdata 2026b.

Original Revision: https://phabricator.services.mozilla.com/D296351

Comment 9

[Phabricator Automation]

firefox-esr140 Uplift Approval Request

• User impact if declined/Reason for urgency: Wrong time zone data when calling standard Date and Intl.DateTimeFormat methods.
• Code covered by automated testing?: yes
• Fix verified in Nightly?: yes
• Needs manual QE testing?: no
• Steps to reproduce for manual QE testing:
• Risk associated with taking this patch: low
• Explanation of risk level: It only updates time zone data files.
• String changes made/needed?: None
• Is Android affected?: yes

Comment 10

[Pulsebot]

https://github.com/mozilla-firefox/firefox/commit/60cb1f68b9a3
https://hg.mozilla.org/releases/mozilla-beta/rev/3ce703c604d7

Comment 11

[Pulsebot]

https://hg.mozilla.org/releases/mozilla-esr140/rev/9f54b2290539

Comment 12

[Pulsebot]

https://hg.mozilla.org/releases/mozilla-esr140/rev/87de097e688c

Comment 13

[Pulsebot]

https://hg.mozilla.org/releases/mozilla-esr140/rev/edbe6d65fb86