At my workplace we use iCal Server running on Mac OS X 10.5 Server to share several calendars all under our one staff group. With iCal, so long as the group is delegated to be shown on the user’s accounts you can see all the calendars but with Sunbird you only get to see the first calendar.
Before going further it’s worth noting how to delegate a group calendar so a user can view it without manually adding the group calendar as it’s own calendar (if using Delegates instead of multiple calendar “accounts” (same credentials, different calendars) is your aim). To do so you have to add the group calendar as a normal account in order to set it up, and then set up delegation as you would for a normal account. The important URL to know for using a group calendar is http://FQDN.OF.SERVER:8008/principals/groups/groupname (as always replace http with https and 8008 with 8443 if you are using SSL).
Sunbird uses slightly different URLs than what you use in iCal to start with, where in iCal an example URL might be http://FQDN.OF.SERVER:8008/principals/users/USERNAME or http://FQDN.OF.SERVER:8008/principals/groups/GROUPNAME. The corresponding URL to use in Sunbird is http://FQDN.OF.SERVER:8008/calendars/users/USERNAME/calendar or http://FQDN.OF.SERVER:8008/calendars/groups/GROUPNAME/calendar
That’s great for adding a single calendar but what if a user or a group has multiple calendars under their one account? iCal will automatically show them as a group whereas Sunbird requires you to add each and everyone that you wish to have show up.
You can specify a “sub-calendar” to subscribe to in Mozilla Sunbird by specifying the unique ID of that calendar instead in the form of the url http://FQDN.OF.SERVER:8008/calendars/__uids__/UID_OF_GROUP_OR_USER/UID_OF_SUB_CALENDAR (Newer versions of Lightning will take http://FQDN.OF.SERVER:8008/users/USERNAME/UID_OF_SUB_CALENDAR). Note the lack of calendar at the end of the URL. To determine the UIDs in question it’s easiest using iCal, if you click on a calendar and press Command-I (File -> Get Info) you can see part of the CalDAV URL at the bottom of the sheet that appears.
You will see calendars/__uids__/UNIQUE_ID/ONLY_PART_OF_THE_UNIQUE_ID because the label the text is placed into is not big enough to fit the URL. Because you can’t get the full URL from there it’s easiest to go to the iCal Server itself and navigate to /Library/CalendarServer/Documents/calendars/__uids__/ (you’ll need administrator privileges to view this). From there find the folder named the same as the UNIQUE_ID portion of the URL and open it to find a folder with the UNIQUE_ID of the “sub-calendar”. You can now put the URL together and use that in Sunbird to view that additional calendar.
Example URL of a sub-calendar in the group:
https://FQDN.OF.SERVER:8443/calendars/__uids__/FA26C8C6-5B78-4AB0-AE73-0E9576574EBB/F74174B7-380C-4630-9192-9025F4C691A2
EDIT:
Sub-calendars also work at https://FQDN.OF.SERVER:8443/calendars/users/USERNAME/UID_OF_SUBCALENDAR
Sources Used: