The most simple (and easiest) way is to use the TB built-in CardDAV support. You'd need to create a new CardDAV address book.

open a new Address Book tab in Thunderbird click the 'Create a new address book' icon at the top left corner of the Address Book tab choose 'Add CardDAV Address Book' provide you Gmail email address for 'Username', and leave the 'Location' field blank enter your Google account password when prompted, and give Thunderbird permissions to access your Google Address Book. Note, cookies need to be temporarily allowed in Thunderbird for this to work.

The new Google Address Book will show up in the left pane of the Address Book tab. You can rename the address book once it has been created.

Thanks for your quick reply. However it is synch of Contacts only that I am looking to solve ... I only use one Calendar which is the Google one. Perhaps you have to synch both Contacts &Calendar?

Apologies, I mixed up Address Book and Calendar. It's fixed now.

Thanks for the correct info ... all sorted.