[Trisquel-users] Re : How connect to Nextcloud Calendar & Contacts with Icedove?

[lcerf]

It should be listed in the add-ons.  It is here.  I am pretty sure it is  
because the "xul-ext-lightning" package is installed.  That said I guess you  
could as well install the Lightning extension from this file (as you did for  
CardBook):  
https://addons.thunderbird.net/thunderbird/downloads/file/633791/lightning-5.4-sm+tb-linux.xpi