Two suggestions for you: a) Google Contacts and the gContactSync add-on. There are some compromises due to differences in the way Thunderbird's Address Book and Google Contacts break down contact details into their component parts. b) Addressbooks Synchronizer and an online storage facility. I use a Dropbox folder, but you could use a folder on an IMAP email account or your own ftp server. Note this isn't a real time synchronization, since updating only occurs as you open and close Thunderbird. I use Thunderbird in two locations (at work and at home) and therefore I never need to run both at the same time, so this works well for me. https://addons.mozilla.org/en-US/thunderbird/addon/gcontactsync/ https://addons.mozilla.org/en-US/thunderbird/addon/addressbooks-synchronizer/