Tasks and/or events are still on the mail pane Rated 5 out of 5 stars

You just need to activate the Today pane, and then toggle to what you want to be displayed (T only/E only/T+E using the arrows at the top of the Today Pane).
A lot of display options have also be moved to the "Display" menu of Thunderbird itself.
Check it out!

This review is for a previous version of the add-on (0.9).