Be able to use a google calendar instead of a Thunderbird calendar

[theperm]

It would be cool if the extensions use an existing Follow-Up calendar instead of creating its own, this way one could use say a google calendar to have their follow-ups in the cloud with the ability to see them on the go from a smartphone.

[saric]

... or any other kind of remote calendar, like CalDAV.

[erenoglu]

Or the Tasks calendar created by Exchange 2007/2012 Tasks & Calendar plugin.