Safari user here—I personally have never used extensions much (probably my own loss), and on Safari I just have 1Password and uBlock°.

Besides Safari's lack of extensions I find it to be more or less on par with Firefox, assuming you're in the Apple ecosystem. The dev tools feel extremely polished and feature complete. The only thing Safari's dev tools lack IMO is no fancy CSS support for things like grid or animations.

I occasional open up Firefox Dev Edition when I get a weird bug on a webpage and that sort of thing but besides that Safari has served all my needs perfectly.