Review for Extra Folder Columns by tbirduser99
Rated 5 out of 5 stars
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.
To create your own collections, you must have a Mozilla Add-ons account.