Custom Tags with Thunderbird stored on IMAP server

Diagnosis:
It is quite common to share one IMAP account with more than one user or more then one device. Thunderbird has predefined Labels called Tags, sometimes called as „default hard-coded“, values are from 0 to 5 and are of following meaning:
0 – Remove all tags,
1 – Important,
2 – Work,
3 – Personal,
4 – To Do,
5 – Later

Adding, editing or deleting any custom tags on the menu> Preferences > Display > Tags works fine unless you go to other device. By default all new custom tags are stored locally in your machine and information will be lost in other device – e.g. not synchronized, because such custom tag is not transmitted to IMAP server.

What we want
Let’s say we have inbox info@mydomain.tld and we have farm of devices and users to use same IMAP account. Our favourite mail client is Thunderbird. We want to set several custom labels, in our example we want to know who is touching mail, so we set this 2 custom labels:
91 – Peter Best
92 – Eva Sweet
How to get synchronized custom labels?

How To

To get all custom tags synchronized to all machines using same IMAP account (our farm of PCs, NBs, mobile smarts, webmail) we need to touch menu > Preferences > Advanced > Config Editor and add additional custom tag arguments
mailnews.tags.$label90.tag and mailnews.tags.$label90.color as shown here:

custom tag about:config

After editing configuration it is possible to edit/delete color and custom label in menu > Preferences > Display > Tags
It is smart idea to use higher numbers in $label## in case Thunderbird’s further version will increase number of predefined tags.
Follow the same procedure on all „farm members“.

This solution was happy enough for us at this moment, fell free to do it similar, but please mind there absolute no guaranty it will work good for you, use your common sense. Good luck!