How to sync labels between Google and Thunderbird contacts?

You are more than welcome to rewrite the article and bring it up to date. I don't have the time or the inclination any longer.

I have no idea what you are talking about with contact and labels. Do Google contact have labels? Apparently they are used for creating mailing lists. I can use Google search. They certainly do not appear in Thunderbird as a mailing list as I just added a label to someone in my gmail contact and no mailing list with a single entry appearing in that address book locally after I syncronised the address book. But that does not suprise me as the contact sync is implemented with carddav which is based on the vcard standard. Vcards do not have mailing lists as a part of their description I do not think.

It appears the tbsync add-on does do something with groups using the Google people API . See https://github.com/zanonmark/Google-4-TbSync#current-status-and-roadmap--known-limitations

The calendar addon provider for google calendar offers tasks. Those are not included in the caldav standard and therefore are not included in the native calendar synchronization.

Thanks for the prompt response! Now it's my turn to plead ignorance! I'm not familiar with Groups, but if they are like maillists, that's not what I am looking for. What I need is to be able to categorize my contacts, e.g. by church, family, personal, professional etc. Outlook calls these Categories. Google calls them Labels. Some other platforms call them tags. I don't care what they're called, as long as they can be ported across platforms. Outlook tries to store its categories in Google's data structure, but often fails. Although both Outlook and Thunderbird do pretty well syncing Google Labels and Mail Folders, Outlook makes no attempt to sync its Categories with Google's Labels. Is there anything I could use in Thunderbird to map to Google's Labels? An add-on would seem superfluous: TB is syncing both Calendar and Contacts with Google without any, and notes in the various Contacts add-ons I found suggest that they either don't work or aren't needed.

See https://support.mozilla.org/en-US/questions/1534403