a client’s thunderbird 3 stopped launching – everytime it would bounce for a bit on the dock and then give a crash report. some googling revealed a few possible fixes, including the deletion of the metadata folder [didn't work] and this fix which did:
Fire up “Terminal.app”
cd Library/Thunderbird/Profiles/
find . -type f -name "*.msf" | xargs -I {} rm {}
all is well.