Rated 5 out of 5 stars

by tbirduser99 on July 22, 2015 ·

In Thunderbird 38.1.0, Folder Pane Columns is a built-in feature.
If you run with the traditional menu bar (selections at the very top of the window), the option is View | Layout | Folder Pane Columns .
If you use the application menu (an icon of three horizontal lines near the upper right of the window), the option is Options | Layout | Folder Pane Columns .
In some localizations, it might be Preferences | Layout | Folder Pane Columns .
But note that under the application menu, the Layout option is *not* under View.

Rated 5 out of 5 stars

by tbirduser99 on March 17, 2010 ·

For the people who want the count of unread messages to be in bold:
Click on the icon to the right of the Size column, and uncheck Unread in the dropdown list. Then Unread will not appear as a column, but the Unread count will appear in bold, in parentheses after the folder name.

This review is for a previous version of the add-on (0.4).