Pale Moon is a continuation of a Firefox fork and still uses old Firefox themes feature as “themes”. Сurrent Firefox themes are not original themes, but merely old “personas” ( https://duckduckgo.com/?q=Firefox+Personas+And+Themes+Difference ), which were renamed several years ago when real themes were removed from the addons.mozilla thing. These old themes allowed any simple person to go to the official website and choose a convenient appearance of the browser. However, Mozilla stopped to like it, and the themes were removed.
Vivaldi is a browser on another engine (Blink). In the current talk about the height, it is important that there is the possibility of reducing the appearance of the entire interface. I don’t like that solution as much as old Firefox themes, but still it is one of the solutions for those who need more of screen space.
I hope Mozilla will be able to return the old solution to addons.mozilla or find a new one. 92 Proton pixels is a lot.