This will copy all of the bookmarks, emails, email filters, settings, etc. for Firefox and Thunderbird. Locate, copy and overwrite the application folders for Firefox and Thunderbird:
Mac:
[user home] /library/Thunderbird
[user home]/library/Application Support/Firefox
PC:
[user home ] /AppData/Roaming/Thunderbird
[ user home] /AppData/Roaming/Mozilla/Firefox
Note:
For PC, AppData folder is a hidden or system folder so it will be hidden by default.