thank you very much for the script, i've done the replacement earlier, but the Thunderbird icons remained the same... i've found out the my TB, for some strange reason, uses the Thunderbird icon located in /usr/share/mozilla-thunderbird/chrome/icons/default . This is also the place for those horrible looking compose / address book / contact icons. So i asked one of my friends for the original icons, renamed and resized them and voila, the ugly icons are gone if someone would like to do this, here are the icons i used.
(note: default.xpm is the Sunbird icon, for the Calendar extension.)
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