webcal:// URLs do not open calendar application

Have you tried registering a custom protocol handler, as described here: https://askubuntu.com/questions/514125/url-protocol-handlers-in-basic-ubuntu-desktop/1023143#1023143 ?

I did try to pass e.g. "webcal://calendar.google.com/calendar/ical/mozilla.com_dbq84anr9i8tcnmhabatstv5co%40group.calendar.google.com/public/basic.ics" to thunderbird on the command line, and it didn't like it (failed to even start). So I doubt there is support for it, at least as a protocol handler. It does seem to know how to import them from within the application though (see https://bugzilla.mozilla.org/show_bug.cgi?id=1427588).

If you want better integration as a protocol handler, I suggest filing a bug at https://bugzilla.mozilla.org/enter_bug.cgi#h=dupes|Thunderbird

I've opened a feature request for thunderbird: https://bugzilla.mozilla.org/show_bug.cgi?id=1754682

The Thunderbird bug has been fixed. It already supported webcal urls, but had a problem when a webcal url ended with .ics as it did in your case. That problem is gone now.

Back to the problem: Firefox should open those URLs with thunderbird.
I think that Firefox on Ubuntu should provide the defaults that it does, and not require me to register something.

https://bazaar.launchpad.net/~mozillateam/thunderbird/thunderbird.jammy/revision/672 should do the trick.

Well, it does allow xdg-open to open thunderbird when passed a webcal:// URL, but it's not enough to instruct firefox to do the same, apparently.

I have tested adding a custom protocol handler in Firefox by creating the following entries in about:config :

  network.protocol-handler.expose.webcal
  network.protocol-handler.external.webcal
  network.protocol-handler.warn-external.webcal

and I did manage to get a new entry for the webcal protocol, but associating it with an external application (either thunderbird or xdg-open) doesn't work in the firefox snap, because the file dialog that is presented to the user to select an application uses the xdg desktop portal which remaps the path to e.g. /run/user/1000/doc/9a5d9a5e/xdg-open.

This needs testing in the firefox deb, with snap confinement out of the way.

Interestingly, in the firefox deb opening webcal:// hyperlinks works OOTB, without any change (after thunderbird has been registered as a handler for them).

I'm going to close the bug task for Firefox, please file an upstream bug at https://bugzilla.mozilla.org/enter_bug.cgi if you care about the snap use case, because that's where we track snap-related issues. Thanks!

This bug was fixed in the package thunderbird - 1:91.6.1+build1-0ubuntu1

---------------
thunderbird (1:91.6.1+build1-0ubuntu1) jammy; urgency=medium

  * New upstream stable release (91.6.1build1)

 -- Olivier Tilloy <email address hidden> Mon, 14 Feb 2022 20:35:29 +0100