This is downvoted but needs to be said. Thunderbird was an amazing 90's style piece of software that has unfortunately been been changed into a more "modern" look, with excessive white space and power-user hostile work flows.
It was near perfect, just needed better search, pretty much.
I liked the old style, too. Nevertheless there is View → Density → Compact / Default / Relaxed.
Exactly. It used to be good and they're making it worse every day.
“90s style” seems to be a compliment in some posts and a negative in others.
Very likely user’s age perspective.
It’s absolutely correct though.