I've searched for years how to improve Thunderbird and his awkward tabs functionality. I found nothing, and had to deal with the left sidepanel and my twelve accounts spaming litteraly my screen.
just today, I came here (again for the thousandth time) to take a look at something new, and... oh god ! I found the graal.
This is just what I always wanted for. It's perfect. there is tons of options, it's a TRUE extension made by professionals.
I managed to simplify Thunderbird like if it was a totally new program, by cleaning the general toolbar and moving it near the menu bar, unchecking the "Mail toolbar" to let the Quickfolder toolbar display correctly, and hidding the left sidepanel. And I even managed to shorten the Quickfolder toolbar by unchecking some stuffs in the options, letting me stack many tabs for all my accounts without reaching the right side of my screen.
Sincerely, it's an amazing work. I'm stunned. BRAVO ! And THANK YOU !
This review is for a previous version of the add-on (4.7.1).
.. if you care about your _main_ menu styling also check out my "menu on top" addon. It also has some mini bookmark option so you can actually add important emails / tabs (just like the QuickFolders reading list, but that one does only do emails)