msgFilterRules.datをコピーしてあげるだけです。
MAC
~/Library/Thunderbird/Profiles/xxxxxxxx.default/ImapMail/mx.xxxxx.com/msgFilterRules.dat
Windows 7
C:\Users\xxxx\AppData\Roaming\Thunderbird\Profiles\xxxxxxxx.default\mx.xxxxx.com\msgFilterRules.dat %APPDATA%\Thunderbird\Profiles\
Windows XP
C:\Documents and Settings\xxxx\Application Data\Thunderbird\Profiles\xxxxxxxx.default\mx.xxxxx.com\msgFilterRules.dat %APPDATA%\Thunderbird\Profiles\