It's not just nostalgia: - the buttons are big - there is high contrasts - sections are clearly delimited I have the current Thunderbird open all day, and I

It's not just nostalgia: - the buttons are big - there is high contrasts - sections are clearly delimited I have the current Thunderbird open all day, and I'm constantly searching for things. It looks much better, much leaner and cleaner. But nothing stands out from the rest, everything is a shade of grey, buttons are flat, section are loosely separated or sometimes merged, labels don't have icons. It's like the debate about cars with touch screen or buttons: the touch screen makes for a much better look, but its usability sucks. It's not just thunderbird. Phone apps, web apps, they all follow trends that have nothing to do with usability. They copy each others in loop, bored designers go one more round (see ubuntu for an extreme example of this), A/B testing tells manager people downloaded your app more because of the pretty UI or screenshots on the short term. But the current design is a usability disaster, and is only partially working because the UI are getting dumbed down more and more. Apps have less and less accessible buttons and menus. It makes you less productive, but it's easier for the average user, thanks to the paradox of choice. Because of this, having a lean UI is not as terrible, since you don't display much on the viewport anyway (e.g: youtube latest changes, or just tik tok). But of course, advanced users pay a price for that. Also, you can't do it for professional software unless you want to render it harder to use. Case in point: Thunderbird.