Welcome to Thunderbird Add-ons.
Add extra features and styles to make Thunderbird your own.Close
Very useful... Rated 5 out of 5 stars
...because it saves essential space. However it does not remove the menu-bar completely, so the bar is still available for those who rarely need it. Allin all every vertically saved pixel is contribution to a better readability of (longer) websites.
P.S.: I borrowed one of your notes for my own extensions ;-)