the title bar is traditionally not a toolbar, and that first toolbar is typically not visible unless you press Alt. Thunderbird has looked like this for the past 20 years, because all other programs used to too.
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It's not the fault of TB itself. E.g. on Unity desktop, as far as I can remember, the menu bar was merged into the title bar and KDE 5.x has the option to have the menu items as an expanding 'hamburger' menu in the title bar (which isn't that nice, but at least something).
ok. thanks. i have mate desktop and that first toolbar is always there so i can close or minimize the window. and i did not have this "spaces" button in earlier versions. the icon also is bizarrely big i think. gives me windows95 vibes.
do xfe next. i have a 4k display and this shit wastes like 240k pixels while looking ugly.