Rated 4 out of 5 stars
This toolbar button does not appear in the toolbar button dialog on Thunderbird Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:22.214.171.124) Gecko/20100512 Thunderbird/3.0.5
In past experience with this toolbar button, it will not mark all messages read when it is invoked while the cursor is over the (new) inbox collection. Therefore, with messages routed to multiple folders for organization by way of message rules, I must still click on each folder and mark all as read.
This and the toolbar fix would make Mark All Read perfect!
Thanks for the efforts.