Nautipolis for Thunderbird: High-quality, solid theme based on icons from art.gnome.org. Fully compatible with from 5.0 upto latest nightly build (currently 27.0a1). Full support for Lightning/calendar.
Default XP theme for ThunderBird 45. (Mail and Lightning calendar) --- After long time of inactivity, Michal Stanke decided not to update xpDefault. I propose to try, and make this version, tested on Vista and Win 8.1.
MicroThunderbird, for Thunderbird. Based on LittleBird, sporting the same screensaving, and with same 'retro' design (8-bit colors). Fully compatible with from 5.0 upto current nightlies. Full support for Lightning/calendar.