Open Thunderbird.
Instead of sellecting any inbox or folder, click the NAME of an account that show in BOLD text.
Look under the "Accounts" heading for the line starting with a gear icon. There is only one icon looking like that on that page.
The exact wording may differs from what I indicated as my version is not in English. The exact title is localised to the language you are using.
Click that line. A new dialog opens up in a new window.
You can now perform the instructions from my previous post.
Electro
November 2014