Thunderbird Calendar aka the Lightning add-on - Quo vadis?

Jörg Knobloch jorgk at
Wed Jul 31 22:19:06 UTC 2019

Hi lovers of Thunderbird and calendaring,

have you ever asked yourself where one of the "productivity components", 
the Thunderbird Calendar is going?

Since TB 38 it's being shipped with Thunderbird on an "opt out" basis, 
lately it even changed its version numbering scheme from (TB version + 
2) / 10 to just using the TB version[1].

But what's happening otherwise?

Long-standing bugs that have been astonishing the community like the 
inability to process more than one invitation per message[2] or the 
ability to double-click ICS attachments and process them[3] haven't been 
addressed for more than a decade now.

Most if not all volunteer Calendar contributors have left, unless 
Thunderbird hired them[4].

The Calendar blog[5] hasn't seen an update in two years.

Bug triaging is lagging behind[6].

The module page[7] is deserted. I've been on the project since 2015 and 
from the people listed on the page, I've only met Philipp, the module owner.

And there are administrative delays that affect Thunderbird as a whole: 
Slow reviews of patches (including those of potential new contributors), 
slow uplift/backport approvals of patches to beta and ESR versions, slow 
Bugzilla administration, delay of many months to provide the Lightning 
add-on at for those using a distribution which 
doesn't package it[8][9].

Apart from the long-standing issues mentioned above, there are also 
questions reaching into the future:

Why not integrate the calendar functionality completely into Thunderbird 
and not ship it as add-on? That would solve endless incompatibility and 
up/downgrade woes[10][11].

The Calendar code is still using XUL overlays. What's the future of 

What about the "Provider for Google Calendar" add-on[13]? Can that be 
retired in favour of CalDAV? The test to make sure it still works has 
been switched off in August 2018[14].

And finally: What's happening with ical.js, the JavaScript library which 
is meant to replace the C++ library libical?

I think the Thunderbird Calendar needs fresh wind and a more pro-active 

Jörg (Thunderbird hacker).

[2] from 2010, patch 
reviewed after almost ONE YEAR(!)
[3] from 2006, 
closed for public comment
[6] - bugs of "major" importance

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