There's a nice aviation Firefox/Firebird & Thunderbird theme at
http://skypilot.projectit.com/
"Sky Pilot Classic is a theme commemorating Charles Lindbergh and the "Spirit of St. Louis" and is a portation of the original Netscape 6.1 theme designed and authored by Kevin Cunningham, aka. kang. It uses a unique blend of purple and grey hues in combination with vivid and striking multi-colored icons which seems to becken one to explore the full features of the browser and its various components."