Whether you are using Linux or not, Thunderbird is a great email client. It’s been around awhile, and works well. But what if we want more than what Thunderbird offers stock? What can we do so that we can share address books between users on completely different computers? Is there a way to use calendars? Can we then share the calendars so other users can access them? With fresh-from-the-box Thunderbird, good luck. Fortunately, the folks at Mozilla have given us the ability to create extensions for this great email client