PNG ICO ICNS MORE
Desktop apps
3D
Mozilla icons
Thunderbird
Black
256x256
48px icons 2
SteelBlue
48x48
DarkCyan
UI
Black and gold
mozilla, Thunderbird
Computer & hardware
FS Icons Ubuntu
512x512
3D Cartoon Icons Pack
300x300
Avatars & smileys
Birdies
bird, Thunderbird
Family & home
Old school by Babasse
Animal, Thunderbird, eagle
128x128
Travel & hotels
Bags and boxes
Human o2
Thunderbird, mozilla
Orb icons
Photography & graphic design
Dark Glass
Nuvola
Email, mozilla, Thunderbird
realistiK Reloaded
DarkSlateBlue
Crystal Clear
Brown