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 ** Bug watch added: Mozilla Bugzilla #1427588 https://bugzilla.mozilla.org/show_bug.cgi?id=1427588 ** Changed in: firefox (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to firefox in Ubuntu. https://bugs.launchpad.net/bugs/1960421 Title: webcal:// URLs do not open calendar application Status in firefox package in Ubuntu: Incomplete Bug description: I have Thunderbird 91.5.0 (64-Bit) installed on Ubuntu 20.04 and use it for calendaring. When clicking on a webcal:// or webcals:// URL in Firefox 96.0 (64-Bit) on Ubuntu 20.04, nothing happens. I expect that Thunderbird opens and asks to subscribe to the calendar. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1960421/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp
