Rated 5 out of 5 stars

As good as this extension is, it is rarely updated when new Thunderbird versions are released. Now that Thunderbird 5 is out we can start using Thunderbird Conversations (adds Gmail-like threading) which actually incorporates a Slideshow-like feature. So for those sick of waiting for Slideshow to be updated, go check out Conversations:

This review is for a previous version of the add-on (1.4.2).  This user has 2 previous reviews of this add-on.