Rated 3 out of 5 stars
Mail headers aren't shown anymore, central Inbox, Sent etc. for all accounts is empty, sometimes it's even not possible to select anything in the menu bar.
Deactivating the addon instantly cured all of these problems, and I also tried deactivating all other addons except Mnenhy. WIth Mnenhy active, TB shows the faulty and erratic behaviour which instantly stops when I deactivate the addon.