new looks and legacy option

Hi Abd, Firefox 157 introduced a major new visual design called Nova, and there isn't currently a supported “legacy” or “classic” appearance option that restores the previous Firefox 156 design. Mozilla has, however, brought back Compact Mode, which makes the tabs and toolbar smaller. You can find it under Settings > General > Browser Layout > Compact. If you specifically want the old Firefox 156 appearance, there are some unsupported about:config workarounds being discussed, but I would not recommend changing those preferences as they can stop working or cause unexpected behaviour after an update. Mozilla also warns that about:config customisations are not officially supported. If you mainly dislike how much space the new design uses, I'd try Compact Mode first.