Mozilla’s Stephen Horlander has released a couple of videos showing the plans for a few Firefox tab tasks like adding a new tab.
And here’s an idea on how tearing a tab to its own window would look like (make sure to right-click on the video and select Full Screen to watch it in full resolution):
Other tasks that could be improved with animation are closing and rearranging tabs in the tab bar. The goal here is to make Firefox “feel” more responsive to the user, and I find this prototypes deliver properly.
More details on Stephen’s blog.