Gnome Shell's calendar allows integration only with Evolution, Thunderbird isn't allowed. This is actually expected, as Thunderbird is primarily mail application. But using Lightning plugin, it is a very good calendar solution, too. So, no easy way to define Thunderbird as default calendar application. After some quick googling, I found the following plugin for Thunderbird. Basically, it synces Thunderbird's calendar with Evolution's, one way, and that's it. When I wanted to install it, I had a small, and unrelated, problem. Namely, I could not find how to install it in Thunderburd?! There was no option in Thunderbird for managing Addons!? After some short Googling I finally realized that the menu option on the upper right hand side (icon with three parallel lines) isn't actually the full menu! I managed to open full Tools menu item by pressing Alt+F.
After I installed this plugin, and restarting Gnome and then Thunderbird, it didn't work So, the next I tried this. But first, I checked what was the current setting:
$ gsettings get org.gnome.desktop.default-applications.office.calendar execOk, now I changed the value using the following command:
'evolution -c calendar'
$ gsettings set org.gnome.desktop.default-applications.office.calendar exec thunderbirdThat didn't work either. It occured to me that the problem might be that I'm using Thunderbird profiles, so I also tried to define a profile in the command:
gsettings set org.gnome.desktop.default-applications.office.calendar exec 'thunderbird -P MyProfile'Still, no luck! Then I went back to the plugin page and saw there that I have to create initial Evolution profile. I tried that too, but again, no luck. Maybe the problem was that I'm not using local calendars but remote ones. But then I realized that there is very easy solution. Namely, I created Evolution profile that is connected to Google calendars and synces with them. Google calendars are, in turn, connected to Thunderbird and everything works!
Yet, I didn't managed to get Thunderbird used when I click on Open Calendar option in the Gnome Shell's clock. Evolution is always used. Note that I tried two things, and both didn't help. First, I tried to define Thunderbird as default Calendar application using gsettings command as described above. Next, I tried to define Thunderbird default Calendar application in menu that is accessed by selecting All setting application, Details button, and there Default applications menu option. Note that Thunderbird isn't shown as a possible Calendar application. That is because its MIME type doesn't specify it as such. To change that I used procedure described here. In short, open file /usr/share/applications/mozilla-thunderbird.desktop in text editor and modify line MimeType so that it is
MimeType=message/rfc822;x-scheme-handler/mailto;text/calendar;text/x-vcard;:Now, close text editor and update database file:
update-desktop-database -qFinally, go to Details button and you'll see Thunderbird is now offered as a Calendar application, too.
In the end, I lost few hours investigating this and trying different solutions. Hopefully, someone will find this useful and will have to waste a lot less time.