Rated 5 out of 5 stars

Nice theme, unfortunately the Persona Switcher add-on isn't available any more, so no light weight theme possible. :(

This review is for a previous version of the add-on (3.5.50). 

Light wight themes are still possible, but right now it takes jumping through a lot of hoops.
Persona Switcher is not abandoned for Thunderbird, a new version will be coming soon.