Sunbird and Lightning Calendars

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Lightning is an add-on extending Thunderbird or Seamonkey to integrate standards-based calendaring. Lightning provides for managing calendar data, subscribing to iCalendar feeds (RFC5545), interacting with calendaring services, chiefly CalDAV (RFC4791), and receiving and sending iTIP/iMIP email invitations (RFC5546/RFC2447).

Sunbird was a standalone, standards-based calendaring application for managing calendar data, subscribing to iCalendar feeds (RFC5545), and interacting with calendaring services, chiefly CalDAV, built with many of the same components as Lightning (and without email integration). It is no longer supported or developed - The Calendar Project has stopped Sunbird development to focus on Lightning, so Lightning is currently a safer choice for new users. And time zone information is no longer updated.

Stable releases of Lightning can be downloaded from the project's web site. See download sites. If you experience slowness or instability you should file a bug report.

  • Make backups periodically: crashes may corrupt calendar data. Local calendar data is located in the user Profile folder (Thunderbird, SeaMonkey, Sunbird):
    • in the preferences file (profileDir/prefs.js) and
    • in the local-calendar database (profileDir/calendar-data/local.sqlite).

Lightning and Sunbird are based on a rewrite of Calendar Extension, which is no longer in active development. Development was originally started at OEOne corporation (Canada, now named Axentra), and later for periods a few developers were supported by Oracle (US), Sun Microsystems (Germany, later aquired by Oracle), and by Mozilla Messaging, as well as by volunteers and donations from around the world.


To follow the progress of Lightning and Sunbird, see the Calendar Weblog.

You can discuss Lightning and Sunbird in mozillaZine's Calendar forum.

Lightning is also discussed in the newsgroup/email-list

(archive, feeds, email, newsgroup for newsreader such as Thunderbird or Seamonkey).

(Unmonitored newsgroup archives:,, old netscape.p.m.calendar.)

For Testers and Developers

Nightly builds for testing are available. For nightly Lightning builds, see its download page.

Developers interested in the project can follow progress and contribute to the newsgroup/email-list

(archive, feeds, email, newsgroup for newsgroup client such as Thunderbird).

Or chat at:


Manual UI tests are recorded at Litmus (product Calendar). Some tests have been automated. Some UI tests are automated in JavaScript using MozMill.

Results of testing capatibility with various CalDAV servers are recorded at


To compile from sources, see Sunbird and Lightning build instructions.


  • See "Release Notes" on the download page for Lightning.
  • See known issues.
  • The bug page on the project website has links that list open bugs in the bug database.

Issue Details

When discussing or reporting issues, be sure to note

  • any Error Console messages associated with the issue (Tools ⇒ Error Console)
  • the Build Id (Help ⇒ About, copy last paragraph with all version numbers)
  • the Operating System version (and window manager version if relevant)
  • the Calendar Provider, if relevant (local SQLite storage, local ics file, remote CalDAV, remote GDATA, remote WebDAV/ics, remote WCAP, or name and version of add-on calendar provider)
  • the Calendar Server and version number, if relevant.